media: staging: media: imx: imx7-media-csi: Drop unneeded pixel format validation

The driver won't accept unsupported pixel formats, there's thus no need
to validate it in imx7_csi_pad_link_validate().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>