irqdomain: Report irq number for NOMAP domains

When using a NOMAP domain, __irq_resolve_mapping() doesn't store
the Linux IRQ number at the address optionally provided by the caller.
While this isn't a huge deal (the returned value is guaranteed
to the hwirq that was passed as a parameter), let's honour the letter
of the API by writing the expected value.

Fixes: d22558dd (“irqdomain: Introduce irq_resolve_mapping()”)
Signed-off-by: NXu Qiang <xuqiang36@huawei.com>
[maz: commit message]
Signed-off-by: NMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220719063641.56541-2-xuqiang36@huawei.com

kernel/irq/irqdomain.c

@@ -910,6 +910,8 @@ struct irq_desc *__irq_resolve_mapping(struct irq_domain *domain,
 			data = irq_domain_get_irq_data(domain, hwirq);
 			if (data && data->hwirq == hwirq)
 				desc = irq_data_to_desc(data);
+			if (irq && desc)
+				*irq = hwirq;
 		}
 
 		return desc;