Invalid csi2 port will break the isys notifier bound ops as it is
trying to access an invalid csi2 sub-device instance based on the
port. It will trigger a mc warning, and it will cause the sensor
driver to unbound an inexistent isys csi2 and crash. Adding a
csi2 port sanity check, return error to avoid such case.

Fixes: f50c4ca0 ("media: intel/ipu6: add the main input system driver")
Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
[Sakari Ailus: Fix spelling of "nports" field.]
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>