kernel/mutex: mutex_is_locked can be boolean

Make mutex_is_locked return bool due to this particular function only
using either one or zero as its return value.

No functional change.

Link: http://lkml.kernel.org/r/1513266622-15860-7-git-send-email-baiyaowei@cmss.chinamobile.com
Signed-off-by: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mutex.h

@@ -138,9 +138,9 @@ extern void __mutex_init(struct mutex *lock, const char *name,
  * mutex_is_locked - is the mutex locked
  * @lock: the mutex to be queried
  *
- * Returns 1 if the mutex is locked, 0 if unlocked.
+ * Returns true if the mutex is locked, false if unlocked.
  */
-static inline int mutex_is_locked(struct mutex *lock)
+static inline bool mutex_is_locked(struct mutex *lock)
 {
 	/*
 	 * XXX think about spin_is_locked