mailbox: Make mbox_chan_ops const

The mailbox controller's channel ops ought to be read-only.  Update
all the mailbox drivers to make their mbox_chan_ops const as well.

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Cc: Ashwin Chaugule <ashwin.chaugule@linaro.org>
Cc: Ley Foon Tan <lftan@altera.com>
Acked-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
index d4cf96f..68c4245 100644
--- a/include/linux/mailbox_controller.h
+++ b/include/linux/mailbox_controller.h
@@ -72,7 +72,7 @@
  */
 struct mbox_controller {
 	struct device *dev;
-	struct mbox_chan_ops *ops;
+	const struct mbox_chan_ops *ops;
 	struct mbox_chan *chans;
 	int num_chans;
 	bool txdone_irq;