err.h: add (missing) unlikely() to IS_ERR_OR_NULL()

IS_ERR_VALUE() already contains it and so we need to add this only to
the !ptr check.  That will allow users of IS_ERR_OR_NULL(), to not add
this compiler flag.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/err.h

@@ -37,7 +37,7 @@ static inline bool __must_check IS_ERR(__force const void *ptr)
 
 static inline bool __must_check IS_ERR_OR_NULL(__force const void *ptr)
 {
-	return !ptr || IS_ERR_VALUE((unsigned long)ptr);
+	return unlikely(!ptr) || IS_ERR_VALUE((unsigned long)ptr);
 }
 
 /**