mapping_set_error: add unlikely()

This is called on a per-page basis and in the vast majority of cases
`error' is zero.

Cc: Guillaume Chazarain <guichaz@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/pagemap.h

@@ -22,7 +22,7 @@
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
 {
-	if (error) {
+	if (unlikely(error)) {
 		if (error == -ENOSPC)
 			set_bit(AS_ENOSPC, &mapping->flags);
 		else