[media] exynos4-is: Set valid initial format on FIMC-IS-ISP subdev pads

Ensure there is a valid initial resolution and pixel format set
at the FIMC-IS-ISP subdev pads.

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>