media: ipu6: isys: Use correct pads for xlate_streams()

The pad argument to v4l2_subdev_state_xlate_streams() is incorrect, static
pad number is used for the source pad even though the pad number is
dependent on the stream. Fix it.

Fixes: 3a5c59ad ("media: ipu6: Rework CSI-2 sub-device streaming control")
Cc: stable@vger.kernel.org
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>