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: NAndrew Bresticker <abrestic@chromium.org>
Cc: Ashwin Chaugule <ashwin.chaugule@linaro.org>
Cc: Ley Foon Tan <lftan@altera.com>
Acked-by: NSuman Anna <s-anna@ti.com>
Signed-off-by: NJassi Brar <jaswinder.singh@linaro.org>