media: imx7: csi: Fix regression for parallel cameras on i.MX6UL

media: imx7: csi: Fix regression for parallel cameras on i.MX6UL

Commit 86e02d07871c ("media: imx5/6/7: csi: Mark a bound video mux as
a CSI mux") made an incorrect assumption that for imx7-media-csi,
the bound subdev must always be a CSI mux. On i.MX6UL/i.MX6ULL there
is no CSI mux at all, so do not return an error when the entity is not a
video mux and assign the IMX_MEDIA_GRP_ID_CSI_MUX group id only when
appropriate.

This is the same approach as done in imx-media-csi.c and it fixes the
csi probe regression on i.MX6UL.

Tested on a imx6ull-evk board.

Fixes: 86e02d07871c ("media: imx5/6/7: csi: Mark a bound video mux as a CSI mux")
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-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>