sched: micro-optimize mmdrop()

micro-optimize mmdrop(). Improves schedule()'s assembly a bit.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 785ec84..cfb6805 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1514,7 +1514,7 @@
 extern void FASTCALL(__mmdrop(struct mm_struct *));
 static inline void mmdrop(struct mm_struct * mm)
 {
-	if (atomic_dec_and_test(&mm->mm_count))
+	if (unlikely(atomic_dec_and_test(&mm->mm_count)))
 		__mmdrop(mm);
 }