[media] exynos4-is: Fix initialization of subdev 'flags' field

Ensure the value of struct v4l2_subdev::flags field as set
in v4l2_subdev_init() is preserved when initializing it in
the subdev drivers.

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>