include/linux/kmemcheck.h: fix a trillion warnings

of the form

include/net/inet_sock.h:208: warning: ISO C90 forbids mixed declarations and code

Cc: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Vegard Nossum <vegard.nossum@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kmemcheck.h

@@ -145,10 +145,12 @@ static inline bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
 
 #define kmemcheck_annotate_bitfield(ptr, name)				\
 	do {								\
+		int _n;							\
+									\
 		if (!ptr)						\
 			break;						\
 									\
-		int _n = (long) &((ptr)->name##_end)			\
+		_n = (long) &((ptr)->name##_end)			\
 			- (long) &((ptr)->name##_begin);		\
 		BUILD_BUG_ON(_n < 0);					\
 									\