[media] exynos4-is: Fix TRY format propagation at MIPI-CSIS subdev

Ensure TRY format is propagated from the sink to source pad.
The format at both pads is always same so the TRY format buffer
for pad 0 is used to hold format for both pads.
While at it remove redundant fmt->pad checking.

Reported-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>