media: ti-vpe: cal: Index CSI-2 port starting at 0

The datasheet numbers the CSI-2 PHYs (external to the CAL) starting from
1, but the PPI inputs to the CAL starting from 0. Update the numbering
scheme for csi2_port to match the datasheet, which also simplifies the
driver by removing the need to constantly subtract 1 from the value.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>