"ftrace: Rework event_create_dir()" triggers boot error messages

[Qian Cai <cai@lca.pw>]

The linux-next commit "ftrace: Rework event_create_dir()” [1] triggers boot warnings
for Clang-build (Clang version 8.0.1) kernels (reproduced on both arm64 and powerpc).
Reverted it (with trivial conflict fixes) on the top of today’s linux-next fixed the issue.

configs:
https://raw.githubusercontent.com/cailca/linux-mm/master/arm64.config
https://raw.githubusercontent.com/cailca/linux-mm/master/powerpc.config

[1] https://lore.kernel.org/lkml/20191111132458.342979914@infradead.org/

[  115.799327][    T1] Registered efivars operations
[  115.849770][    T1] clocksource: Switched to clocksource arch_sys_counter
[  115.901145][    T1] Could not initialize trace point events/sys_enter_rt_sigreturn
[  115.908854][    T1] Could not create directory for event sys_enter_rt_sigreturn
[  115.998949][    T1] Could not initialize trace point events/sys_enter_restart_syscall
[  116.006802][    T1] Could not create directory for event sys_enter_restart_syscall
[  116.062702][    T1] Could not initialize trace point events/sys_enter_getpid
[  116.069828][    T1] Could not create directory for event sys_enter_getpid
[  116.078058][    T1] Could not initialize trace point events/sys_enter_gettid
[  116.085181][    T1] Could not create directory for event sys_enter_gettid
[  116.093405][    T1] Could not initialize trace point events/sys_enter_getppid
[  116.100612][    T1] Could not create directory for event sys_enter_getppid
[  116.108989][    T1] Could not initialize trace point events/sys_enter_getuid
[  116.116058][    T1] Could not create directory for event sys_enter_getuid
[  116.124250][    T1] Could not initialize trace point events/sys_enter_geteuid
[  116.131457][    T1] Could not create directory for event sys_enter_geteuid
[  116.139840][    T1] Could not initialize trace point events/sys_enter_getgid
[  116.146908][    T1] Could not create directory for event sys_enter_getgid
[  116.155163][    T1] Could not initialize trace point events/sys_enter_getegid
[  116.162370][    T1] Could not create directory for event sys_enter_getegid
[  116.178015][    T1] Could not initialize trace point events/sys_enter_setsid
[  116.185138][    T1] Could not create directory for event sys_enter_setsid
[  116.269307][    T1] Could not initialize trace point events/sys_enter_sched_yield
[  116.276811][    T1] Could not create directory for event sys_enter_sched_yield
[  116.527652][    T1] Could not initialize trace point events/sys_enter_munlockall
[  116.535126][    T1] Could not create directory for event sys_enter_munlockall
[  116.622096][    T1] Could not initialize trace point events/sys_enter_vhangup
[  116.629307][    T1] Could not create directory for event sys_enter_vhangup
[  116.783867][    T1] Could not initialize trace point events/sys_enter_sync
[  116.790819][    T1] Could not create directory for event sys_enter_sync
[  117.723402][    T1] pnp: PnP ACPI init
[  117.736379][    T1] system 00:00: [mem 0x30000000-0x3fffffff window] could not be reserved
[  126.020353][    T1] pnp: PnP ACPI: found 1 devices
[  126.093919][    T1] NET: Registered protocol family 2
[  126.180007][    T1] tcp_listen_portaddr_hash hash table entries: 65536 (order: 6, 4718592 bytes, vmalloc)
[  126.206510][    T1] TCP established hash table entries: 524288 (order: 6, 4194304 bytes, vmalloc)
[  126.227766][    T1] TCP bind hash table entries: 65536 (order: 6, 4194304 bytes, vmalloc)
[  126.240146][    T1] TCP: Hash tables configured (established 524288 bind 65536)