[media] media: platform: xilinx: xilinx-tpg: constify v4l2_subdev_* structures

[media] media: platform: xilinx: xilinx-tpg: constify v4l2_subdev_* structures

v4l2_subdev_{core/pad/video}_ops structures are stored in the
fields of the v4l2_subdev_ops structure which are of type const.
Also, v4l2_subdev_ops structure is passed to a function
having its argument of type const. As these structures are never
modified, so declare them as const.
Done using Coccinelle: (One of the scripts used)

@r1 disable optional_qualifier @
identifier i;
position p;
@@
static struct v4l2_subdev_video_ops i@p = {...};

@ok1@
identifier r1.i;
position p;
struct v4l2_subdev_ops obj;
@@
obj.video=&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 v4l2_subdev_video_ops i;

File size before:
   text	   data	    bss	    dec	    hex	filename
   6170	   2752	    144	   9066	   236a media/platform/xilinx/xilinx-tpg.o

File size after:
   text	   data	    bss	    dec	    hex	filename
   6666	   2384	      8	   9058	   2362 media/platform/xilinx/xilinx-tpg.o

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>