mailbox: Fix unneeded backport

v3.14 has reinit_completion()

Signed-off-by: Mark Brown <broonie@linaro.org>
diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index 9a937ef..63ecc17 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -252,7 +252,7 @@
 
 	msg_submit(chan);
 
-	INIT_COMPLETION(chan->tx_complete);
+	reinit_completion(&chan->tx_complete);
 
 	if (chan->txdone_method	== TXDONE_BY_POLL)
 		poll_txdone((unsigned long)chan->mbox);