[media] Staging: media: bcm2048: defined region_configs[] array as const array

This patch defines region_configs[] array as const array since it
is not changed anywhere in code.

Signed-off-by: Claudiu Beznea <claudiu.beznea@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>