irqdomain: um: use irq_domain_create_linear() helper

um_pci_init() open-codes what the irq_domain_create_linear() helper
does already. Use the helper instead of open-coding it.

This needs retval checking modification.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: linux-um@lists.infradead.org
Link: https://patch.msgid.link/20250415104713.106819-1-jirislaby@kernel.org


Signed-off-by: Johannes Berg <johannes.berg@intel.com>