dm integrity: fix to not disable/enable interrupts from interrupt context

Use spin_lock_irqsave and spin_unlock_irqrestore rather than
spin_{lock,unlock}_irq in submit_flush_bio().

Otherwise lockdep issues the following warning:
  DEBUG_LOCKS_WARN_ON(current->hardirq_context)
  WARNING: CPU: 1 PID: 0 at kernel/locking/lockdep.c:2748 trace_hardirqs_on_caller+0x107/0x180
Reported-by: Ondrej Kozina <okozina@redhat.com>
Tested-by: Ondrej Kozina <okozina@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>

drivers/md/dm-integrity.c

@@ -1105,10 +1105,13 @@ static void schedule_autocommit(struct dm_integrity_c *ic)
 static void submit_flush_bio(struct dm_integrity_c *ic, struct dm_integrity_io *dio)
 {
 	struct bio *bio;
-	spin_lock_irq(&ic->endio_wait.lock);
+	unsigned long flags;
+
+	spin_lock_irqsave(&ic->endio_wait.lock, flags);
 	bio = dm_bio_from_per_bio_data(dio, sizeof(struct dm_integrity_io));
 	bio_list_add(&ic->flush_bio_list, bio);
-	spin_unlock_irq(&ic->endio_wait.lock);
+	spin_unlock_irqrestore(&ic->endio_wait.lock, flags);
+
 	queue_work(ic->commit_wq, &ic->commit_work);
 }