Build breakage if !SYSFS

[Ralf Baechle <ralf@linux-mips.org>]

Changeset 5cb350baf580017da38199625b7365b1763d7180 causes build breakage
if sysfs support is disabled:

kernel/built-in.o: In function `uids_kobject_init':
(.init.text+0x1488): undefined reference to `kernel_subsys'
kernel/built-in.o: In function `uids_kobject_init':
(.init.text+0x1490): undefined reference to `kernel_subsys'
kernel/built-in.o: In function `uids_kobject_init':
(.init.text+0x1480): undefined reference to `kernel_subsys'
kernel/built-in.o: In function `uids_kobject_init':
(.init.text+0x1494): undefined reference to `kernel_subsys'

This breaks for example mipssim_defconfig.

  Ralf