media: mei: csi: Put the IPU device reference

The mei csi's probe function obtains a reference to the IPU device but
never puts that reference. Do that now.

Fixes: 33116eb1 ("media: ivsc: csi: Use IPU bridge")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>