media: imx: imx7-media-csi: Fix source type identification

media: imx: imx7-media-csi: Fix source type identification

The code in imx7_csi_pad_link_validate() that checks the type of the
source incorrectly handles devices that have no parallel input. In that
case, the source entity of the CSI is the CSI-2 receiver, not the video
mux, and the driver will proceed to check the type of the source of the
CSI-2 receiver.

Make the code more explicit to fix this, by handling the three cases
(parallel input only, CSI-2 receiver only, and video mux) separately.

Note that the driver will not correctly handle the case where only a
parallel input is present, and the external entity connected to the
parallel input reports a MEDIA_ENT_F_VID_IF_BRIDGE or
MEDIA_ENT_F_VID_MUX function. This was broken already, and should be
fixed separately.

Fixes: f5ffb81f5137 ("media: imx7: csi: Fix pad link validation")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>