Replace the old register_chrdev with the more flexible register_chrdev_region.

Ensure that the release() is called when the very last chardev usage was
released, and not when the sysfs devices were removed. This should simplify
hotpluggable drivers considerably.
Tested-by: NMike Isely <isely@isely.net>
Tested-by: NLaurent Pinchart <laurent.pinchart@skynet.be>
Signed-off-by: NHans Verkuil <hverkuil@xs4all.nl>
Acked-by: NDavid Ellingsworth <david@identd.dyndns.org>
Reviewed-by: NHans de Goede <j.w.r.degoede@hhs.nl>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>