gpio: mvebu: Slightly optimize mvebu_gpio_irq_handler()

In the main loop of mvebu_gpio_irq_handler() some calls to
irq_find_mapping() can be saved.

There is no point to find an irq number before checking if this something
has to be done.
By testing first, some calls can be saved.

Signed-off-by: Christophe JAILLET <[e-mail]>
Link: https://lore.kernel.org/r/7190f5def0[e-mail]
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-mvebu.c

···
 	for (i = 0; i < mvchip->chip.ngpio; i++) {
 		int irq;
 
-		irq = irq_find_mapping(mvchip->domain, i);
-
 		if (!(cause & BIT(i)))
 			continue;
 
+		irq = irq_find_mapping(mvchip->domain, i);
 		type = irq_get_trigger_type(irq);
 		if ((type & IRQ_TYPE_SENSE_MASK) == IRQ_TYPE_EDGE_BOTH) {
 			/* Swap polarity (race with GPIO line) */