The probe() function is large. Make it more readable by factoring the
subdev initialization code out. While at it, rename the error labels as
the "free_" prefix isn't accurate.

No functional change intended.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>