fs/xfs/quota: Add missing mutex_unlock

Author: Julia Lawall <julia@diku.dk>

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/)

// 
@@
expression E1;
@@

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

Signed-off-by: Julia Lawall 
Signed-off-by: Alex Elder 

---
 fs/xfs/quota/xfs_qm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
 
diff --git a/fs/xfs/quota/xfs_qm.c b/fs/xfs/quota/xfs_qm.c
index 38e7641..2d8b7bc 100644
--- a/fs/xfs/quota/xfs_qm.c
+++ b/fs/xfs/quota/xfs_qm.c
@@ -249,8 +249,10 @@ xfs_qm_hold_quotafs_ref(
 
 	if (!xfs_Gqm) {
 		xfs_Gqm = xfs_Gqm_init();
-		if (!xfs_Gqm)
+		if (!xfs_Gqm) {
+			mutex_unlock(&xfs_Gqm_lock);
 			return ENOMEM;
+		}
 	}
 
 	/*