serial: 8250_rsa: simplify rsa8250_{request/release}_resource()

* Use already defined 'port' for fetching start/offset, and size.
* Return from the switch immediately -- so it is clear what is returned
  and when.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20250317070046.24386-29-jirislaby@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>