mailbox: constify mbox_chan_ops structures

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>