pps: change pps_class to a const struct

pps: change pps_class to a const struct

The class_create() call has been deprecated in favor of class_register()
as the driver core now allows for a struct class to be in read-only
memory. Change pps_class to be a const struct class and drop the
class_create() call.

Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jori Koolstra <jkoolstra@xs4all.nl>
Acked-by: Rodolfo Giometti <giometti@enneenne.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/20260302151132.3302993-1-jkoolstra@xs4all.nl
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>