[media] media: coda: add const qualifiers

The commit 98d7bbb9 changed *of_device_id.data to const
which introduced warnings in various places that have mostly
been fixed. This patch fixes one such warning by introducing
two const qualifiers.

GCC warning:
drivers/media/platform/coda.c:1785:16: warning:
        assignment discards ‘const’ qualifier
        from pointer target type [enabled by default]

Signed-off-by: Emil Goode <emilgoode@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>