irqchip/armada-370-xp: Use mpic_is_ipi_available() in mpic_of_init()

mpic_of_init() contains the last case where the open coded IPI support
condition needs to be replaced with mpic_is_ipi_available() to keep the
code consistent.

Signed-off-by: Marek Behún <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>

drivers/irqchip/irq-armada-370-xp.c

···
 		return err;
 	}
 
-	if (mpic->parent_irq <= 0) {
+	if (mpic_is_ipi_available(mpic)) {
 		irq_set_default_host(mpic->domain);
 		set_handle_irq(mpic_handle_irq);
 #ifdef CONFIG_SMP