[PATCH -next v3] arm64: mm: Fix unused variable warning in zone_sizes_init

[Nathan Chancellor <natechancellor@gmail.com>]

When building arm64 allnoconfig, CONFIG_ZONE_DMA and CONFIG_ZONE_DMA32
get disabled so there is a warning about max_dma being unused.

../arch/arm64/mm/init.c:215:16: warning: unused variable 'max_dma'
[-Wunused-variable]
        unsigned long max_dma = min;
                      ^
1 warning generated.

Add __maybe_unused to make this clear to the compiler.

Fixes: 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32")
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---

v1 -> v2:

* Fix check for CONFIG_ZONE_DMA32 as pointed out by Will.

v2 -> v3:

* Use __maybe_unused attribute instead of preprocessor ifdefs
  to conform to section 21 of the coding style as pointed out by
  Catalin.

 arch/arm64/mm/init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 44f07fdf7a59..71b45c58218b 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -212,7 +212,7 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 	struct memblock_region *reg;
 	unsigned long zone_size[MAX_NR_ZONES], zhole_size[MAX_NR_ZONES];
 	unsigned long max_dma32 = min;
-	unsigned long max_dma = min;
+	unsigned long __maybe_unused max_dma = min;
 
 	memset(zone_size, 0, sizeof(zone_size));
 
-- 
2.23.0