irqdesc: Fix __handle_domain_irq() comment

It appears that the comment about a NULL domain meaning anything
has always been wrong. Fix it.
Signed-off-by: Marc Zyngier <maz@kernel.org>

include/linux/irqdesc.h

@@ -165,8 +165,7 @@ int generic_handle_irq(unsigned int irq);
 /*
  * Convert a HW interrupt number to a logical one using a IRQ domain,
  * and handle the result interrupt number. Return -EINVAL if
- * conversion failed. Providing a NULL domain indicates that the
- * conversion has already been done.
+ * conversion failed.
  */
 int __handle_domain_irq(struct irq_domain *domain, unsigned int hwirq,
 			bool lookup, struct pt_regs *regs);