blkcg: change a spin_lock() to spin_lock_irq()

Smatch complains that we re-enable IRQs twice.  It looks like we forgot
to disable them here on the spin_trylock() failure path.  This was added
in 9f13ef67 "blkcg: use double locking instead of RCU for blkg
synchronization".

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>`
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/blk-cgroup.c

@@ -1601,7 +1601,7 @@ static int blkiocg_pre_destroy(struct cgroup_subsys *subsys,
 		} else {
 			spin_unlock_irq(&blkcg->lock);
 			cpu_relax();
-			spin_lock(&blkcg->lock);
+			spin_lock_irq(&blkcg->lock);
 		}
 	}