fs/xfs/quota: Add missing mutex_unlock

Add a mutex_unlock missing on the error path. The use of this lock
is balanced elsewhere in the file.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression E1;
@@

* mutex_lock(E1,...);
<+... when != E1
if (...) {
... when != E1
* return ...;
}
...+>
* mutex_unlock(E1,...);
// </smpl>

Signed-off-by: Julia Lawall <[e-mail]>
Signed-off-by: Alex Elder <[e-mail]>

fs/xfs/quota/xfs_qm.c

···
 
 	if (!xfs_Gqm) {
 		xfs_Gqm = xfs_Gqm_init();
-		if (!xfs_Gqm)
+		if (!xfs_Gqm) {
+			mutex_unlock(&xfs_Gqm_lock);
 			return ENOMEM;
+		}
 	}
 
 	/*