Mailbox: flush pending deferred works before freeing blk queue

flush pending deferred works before freeing blk_queue to prevent
any attempt of access to blk_queue after it was freed

Signed-off-by: Fernando Guzman Lugo <x0095840@ti.com>
Signed-off-by: Hiroshi DOYU <Hiroshi.DOYU@nokia.com>

arch/arm/plat-omap/mailbox.c

@@ -299,6 +299,8 @@ static int omap_mbox_startup(struct omap_mbox *mbox)
 static void omap_mbox_fini(struct omap_mbox *mbox)
 {
 	free_irq(mbox->irq, mbox);
+	tasklet_kill(&mbox->txq->tasklet);
+	flush_work(&mbox->rxq->work);
 	mbox_queue_free(mbox->txq);
 	mbox_queue_free(mbox->rxq);