[media] media: mt9m111: use only the SRGB colorspace

mt9m111 being a camera sensor, its colorspace should always be SRGB, for
both RGB based formats or YCbCr based ones.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>