media: imx: imx7-mipi-csis: Implement get_fwnode_pad op

Use v4l2_subdev_get_fwnode_pad_1_to_1() as the get_fwnode_pad operation.
The imx7-mipi-csis maps port numbers and pad indexes 1:1.

Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>