irq: mips: simplify do_domain_IRQ()

There's no need fpr arch/mips's do_domain_IRQ() to open-code the NULL
check performed by handle_irq_desc(), nor the resolution of the desc
performed by generic_handle_domain_irq().

Use generic_handle_domain_irq() directly, as this is functioanlly
equivalent and clearer.

There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>

arch/mips/kernel/irq.c

@@ -115,11 +115,7 @@ void __irq_entry do_domain_IRQ(struct irq_domain *domain, unsigned int hwirq)
 
 	irq_enter();
 	check_stack_overflow();
-
-	desc = irq_resolve_mapping(domain, hwirq);
-	if (likely(desc))
-		handle_irq_desc(desc);
-
+	generic_handle_domain_irq(domain, hwirq);
 	irq_exit();
 }
 #endif