arm64: cmpxchg: Include build_bug.h instead of bug.h for BUILD_BUG

Having asm/cmpxchg.h pull in linux/bug.h is problematic because this
ends up pulling in the atomic bitops which themselves may be built on
top of atomic.h and cmpxchg.h.

Instead, just include build_bug.h for the definition of BUILD_BUG.
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/include/asm/cmpxchg.h

@@ -18,7 +18,7 @@
 #ifndef __ASM_CMPXCHG_H
 #define __ASM_CMPXCHG_H
 
-#include <linux/bug.h>
+#include <linux/build_bug.h>
 
 #include <asm/atomic.h>
 #include <asm/barrier.h>