word-at-a-time: simplify big-endian zero_bytemask macro

This is simpler and cleaner.  Depending on architecture, a smart
compiler may or may not generate the same code.
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/asm-generic/word-at-a-time.h

@@ -50,7 +50,7 @@ static inline bool has_zero(unsigned long val, unsigned long *data, const struct
 }
 
 #ifndef zero_bytemask
-#define zero_bytemask(mask) (~0ul << __fls(mask) << 1)
+#define zero_bytemask(mask) (~1ul << __fls(mask))
 #endif
 
 #endif /* _ASM_WORD_AT_A_TIME_H */