[media] v4l2-ctrls: use const char * const * for the menu arrays

This prevents checkpatch warnings generated when defining
'static const char *foo[]' arrays. It makes sense to use
const char * const * anyway since the pointers in the array
are indeed const.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>