[media] exynos4-is: Fix reported colorspace at FIMC-IS-ISP subdev

The FIMC-IS-ISP handles only Bayer formats thus V4L2_COLORSPACE_SRGB
should be used. This change applies to the code first added in v3.10.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>