[media] media: vb2: fix incorrect v4l2_buffer->flags handling

Videobuf2 core assumes that driver doesn't set any buffer flags.
This is correct for buffer state flags that videobuf2 manages,
but the other flags like V4L2_BUF_FLAG_{KEY,P,B}FRAME,
V4L2_BUF_FLAG_TIMECODE and V4L2_BUF_FLAG_INPUT should be passed from or to
the driver.

Reported-by: Jonghun Han <jonghun.han@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
CC: Pawel Osciak <pawel@osciak.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>