[media] media: i2c: m5mols: m5mols_core: constify v4l2_subdev_pad_ops structures

v4l2_subdev_pad_ops structures are stored in the pad field
of the v4l2_subdev_ops structure and this field is of type const.
As the v4l2_subdev_pad_ops structures are never modified, they can be
declared as const.
Done using Coccinelle:

@r1 disable optional_qualifier @
identifier i;
position p;
@@
static struct v4l2_subdev_pad_ops i@p = {...};

@ok1@
identifier r1.i;
position p;
struct v4l2_subdev_ops obj;
@@
obj.pad=&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_pad_ops i;

File size before:
 text	   data	    bss	    dec	    hex	filename
   7633	    512	     20	   8165	   1fe5	media/i2c/m5mols/m5mols_core.o

File size after:
  text	   data	    bss	    dec	    hex	filename
   7761	    384	     20	   8165	   1fe5	media/i2c/m5mols/m5mols_core.o

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>