Updated ambiguous comment in pthread_mutex_lock.

The comment used the phrase "normal case" when it more specifically refers to the "recursive case," so I changed it to that.

Change-Id: I8335cce4dee933c6a463aee653b28bd986b5b5e4
diff --git a/libc/bionic/pthread_mutex.cpp b/libc/bionic/pthread_mutex.cpp
index 27ed3e1..bed03ac 100644
--- a/libc/bionic/pthread_mutex.cpp
+++ b/libc/bionic/pthread_mutex.cpp
@@ -451,7 +451,7 @@
     mtype = (mvalue & MUTEX_TYPE_MASK);
     shared = (mvalue & MUTEX_SHARED_MASK);
 
-    /* Handle normal case first */
+    /* Handle non-recursive case first */
     if ( __predict_true(mtype == MUTEX_TYPE_BITS_NORMAL) ) {
         _normal_lock(mutex, shared);
         return 0;