irqdomain: Cleanup domain name allocation

irq_domain_set_name() is truly unreadable gunk. Clean it up before adding
more.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/all/874j7uvkbm.ffs@tglx