nmmgr: Check return code of mutex_lock_irqsafe()

The return value of mutex_lock_irqsafe() should always be checked. If
the locking failed, we will get an imbalance when we get to the
mutex_unlock().

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

Author: pcercuei

kernel/exports/nmmgr.c

@@ -82,7 +82,8 @@ int nmmgr_handler_remove(nmmgr_handler_t *hnd) {
     nmmgr_handler_t *c, *tmp;
     int rv = -1;
 
-    mutex_lock_irqsafe(&mutex);
+    if(mutex_lock_irqsafe(&mutex) < 0)
+        return -1;
 
     /* Verify that it's actually in there */
     LIST_FOREACH_SAFE(c, &nmmgr_handlers, list_ent, tmp) {