[PATCH] s390: fix -Wundef warning for CONFIG_KERNEL_ZSTD

[Masahiro Yamada <masahiroy@kernel.org>]

Since commit 80b6093b55e3 ("kbuild: add -Wundef to KBUILD_CPPFLAGS
for W=1 builds"), building with W=1 detects misuse of #(el)if.

  $ make W=1 ARCH=s390 CROSS_COMPILE=s390x-linux-gnu-
    [snip]
  arch/s390/boot/decompressor.c:28:7: warning: "CONFIG_KERNEL_ZSTD" is not defined, evaluates to 0 [-Wundef]
     28 | #elif CONFIG_KERNEL_ZSTD
        |       ^~~~~~~~~~~~~~~~~~

This issue has been hidden because arch/s390/boot/Makefile overwrites
KBUILD_CFLAGS, dropping -Wundef.

CONFIG_KERNEL_ZSTD is a bool option. #elif defined() should be used.

The line #ifdef CONFIG_KERNEL_BZIP2 is fine, but I changed it for
consistency.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 arch/s390/boot/decompressor.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/s390/boot/decompressor.c b/arch/s390/boot/decompressor.c
index e27c2140d620..8dcd7af2911a 100644
--- a/arch/s390/boot/decompressor.c
+++ b/arch/s390/boot/decompressor.c
@@ -23,9 +23,9 @@
 #define memmove memmove
 #define memzero(s, n) memset((s), 0, (n))
 
-#ifdef CONFIG_KERNEL_BZIP2
+#if defined(CONFIG_KERNEL_BZIP2)
 #define BOOT_HEAP_SIZE	0x400000
-#elif CONFIG_KERNEL_ZSTD
+#elif defined(CONFIG_KERNEL_ZSTD)
 #define BOOT_HEAP_SIZE	0x30000
 #else
 #define BOOT_HEAP_SIZE	0x10000
-- 
2.34.1