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 <[e-mail]>
Cc: Ashwin Chaugule <[e-mail]>
Cc: Ley Foon Tan <[e-mail]>
Acked-by: Suman Anna <[e-mail]>
Signed-off-by: Jassi Brar <[e-mail]>

drivers/mailbox/arm_mhu.c

···
 	free_irq(mlink->irq, chan);
 }
 
-static struct mbox_chan_ops mhu_ops = {
+static const struct mbox_chan_ops mhu_ops = {
 	.send_data = mhu_send_data,
 	.startup = mhu_startup,
 	.shutdown = mhu_shutdown,

drivers/mailbox/mailbox-altera.c

···
 	}
 }
 
-static struct mbox_chan_ops altera_mbox_ops = {
+static const struct mbox_chan_ops altera_mbox_ops = {
 	.send_data = altera_mbox_send_data,
 	.startup = altera_mbox_startup,
 	.shutdown = altera_mbox_shutdown,

drivers/mailbox/omap-mailbox.c

···
 	return ret;
 }
 
-static struct mbox_chan_ops omap_mbox_chan_ops = {
+static const struct mbox_chan_ops omap_mbox_chan_ops = {
 	.startup        = omap_mbox_chan_startup,
 	.send_data      = omap_mbox_chan_send_data,
 	.shutdown       = omap_mbox_chan_shutdown,

drivers/mailbox/pcc.c

···
 	return 0;
 }
 
-static struct mbox_chan_ops pcc_chan_ops = {
+static const struct mbox_chan_ops pcc_chan_ops = {
 	.send_data = pcc_send_data,
 };
 

include/linux/mailbox_controller.h

···
  */
 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;