media: ipu3-cio2: Allow probe to succeed if there are no sensors connected

The device won't be powered off on systems that have no sensors connected
unless it has a driver bound to it. Allow that to happen even if there are
no sensors connected to cio2.

Reviewed-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@linux.intel.com>
Tested-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>