[media] s5p-jpeg: Adjust g_volatile_ctrl callback to Exynos4x12 needs

Whereas S5PC210 device produces decoded JPEG subsampling values that
map on V4L2_JPEG_CHROMA_SUBSAMPLNG values, the Exynos4x12 device
doesn't. This patch adds helper function s5p_jpeg_to_user_subsampling,
which performs suitable translation.

Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>