mailbox: constify mbox_chan_ops structures

Check for mbox_chan_ops structures that are only stored in the ops field
of a mbox_controller structure. This field is of type const struct
mbox_chan_ops *, so mbox_chan_ops structures having this property can be
declared as const.
Done using Coccinelle:

@r1 disable optional_qualifier @
identifier i;
position p;
@@
struct mbox_chan_ops i@p = {...};

@ok1@
identifier r1.i;
struct hi6220_mbox mbox;
struct slimpro_mbox ctx;
position p;
@@
(
mbox.controller.ops=&i@p
|
ctx.mb_ctrl.ops=&i@p
)

@bad@
position p!={r1.p,ok1.p};
identifier r1.i;
@@
i@p

@depends on !bad disable optional_qualifier@
identifier r1.i;
@@
+const
struct mbox_chan_ops i;

File size details:

   text	   data	    bss	    dec	    hex	filename
   2310	    248	      0	   2558	    9fe	drivers/mailbox/hi6220-mailbox.o
   2366	    192	      0	   2558	    9fe	drivers/mailbox/hi6220-mailbox.o

   1500	    248	      0	   1748	    6d4 mailbox/mailbox-xgene-slimpro.o
   1556	    192	      0	   1748	    6d4 mailbox/mailbox-xgene-slimpro.o
Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/hi6220-mailbox.c

@@ -221,7 +221,7 @@ static void hi6220_mbox_shutdown(struct mbox_chan *chan)
 	mbox->irq_map_chan[mchan->ack_irq] = NULL;
 }
 
-static struct mbox_chan_ops hi6220_mbox_ops = {
+static const struct mbox_chan_ops hi6220_mbox_ops = {
 	.send_data    = hi6220_mbox_send_data,
 	.startup      = hi6220_mbox_startup,
 	.shutdown     = hi6220_mbox_shutdown,

drivers/mailbox/mailbox-xgene-slimpro.c

@@ -174,7 +174,7 @@ static void slimpro_mbox_shutdown(struct mbox_chan *chan)
 	devm_free_irq(mb_chan->dev, mb_chan->irq, mb_chan);
 }
 
-static struct mbox_chan_ops slimpro_mbox_ops = {
+static const struct mbox_chan_ops slimpro_mbox_ops = {
 	.send_data = slimpro_mbox_send_data,
 	.startup = slimpro_mbox_startup,
 	.shutdown = slimpro_mbox_shutdown,