drivers: rpmsg: class_destroy() is deprecated

drivers: rpmsg: class_destroy() is deprecated

The class_destroy() function documents that:

  Note, the pointer to be destroyed must have been created with a call
  to class_create().

However, class_create() is deprecated. rpmsg already uses
class_register() but the class_destroy() calls should also be replaced
with class_unregister().

Link: https://lore.kernel.org/all/2023040244-duffel-pushpin-f738@gregkh/
Signed-off-by: Jori Koolstra <jkoolstra@xs4all.nl>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20260308140850.1138376-1-jkoolstra@xs4all.nl
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>