Use storeRelease to unlock a mutex instead of fetchAndStoreRelease

We're not checking the result anyway, so use a simpler operation.

Change-Id: I8c2db35be86660b29d81dd97ce3e269de55a37df
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

src/corelib/thread/qmutex_linux.cpp

@@ -244,7 +244,7 @@ void QBasicMutex::unlockInternal() Q_DECL_NOTHROW
     Q_UNUSED(d);
     Q_ASSERT(!isRecursive());
 
-    d_ptr.fetchAndStoreRelease(0);
+    d_ptr.storeRelease(0);
     _q_futex(&d_ptr, FUTEX_WAKE, 1, 0);
 }