gpio: mlxbf2: use platform_get_irq_optional()

The gpio-mlxbf2 driver interfaces with four GPIO controllers,
device instances 0-3. There are two IRQ resources shared between
the four controllers, and they are found in the ACPI table for
instances 0 and 3. The driver should not use platform_get_irq(),
otherwise this error is logged when probing instances 1 and 2:
mlxbf2_gpio MLNXBF22:01: error -ENXIO: IRQ index 0 not found

Fixes: 2b725265cb08 ("gpio: mlxbf2: Introduce IRQ support")
Cc: [e-mail]
Signed-off-by: David Thompson <[e-mail]>
Reviewed-by: Shravan Kumar Ramani <[e-mail]>
Reviewed-by: Mika Westerberg <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-mlxbf2.c

···
 	gc->ngpio = npins;
 	gc->owner = THIS_MODULE;
 
-	irq = platform_get_irq(pdev, 0);
+	irq = platform_get_irq_optional(pdev, 0);
 	if (irq >= 0) {
 		girq = &gs->gc.irq;
 		gpio_irq_chip_set_chip(girq, &mlxbf2_gpio_irq_chip);