sched/Documentation: Remove unneeded word

The second 'mutex' shouldn't be there, it can't be about the mutex,
as the mutex can't be freed, but unlocked, the memory where the
mutex resides however, can be freed.
Signed-off-by: Sharon Dvir <sharon.dvir1@mail.huji.ac.il>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1422827252-31363-1-git-send-email-sharon.dvir1@mail.huji.ac.ilSigned-off-by: Ingo Molnar <mingo@kernel.org>

kernel/locking/mutex.c

@@ -81,7 +81,7 @@ __visible void __sched __mutex_lock_slowpath(atomic_t *lock_count);
  * The mutex must later on be released by the same task that
  * acquired it. Recursive locking is not allowed. The task
  * may not exit without first unlocking the mutex. Also, kernel
- * memory where the mutex resides mutex must not be freed with
+ * memory where the mutex resides must not be freed with
  * the mutex still locked. The mutex must first be initialized
  * (or statically defined) before it can be locked. memset()-ing
  * the mutex to 0 is not allowed.