gpio: 104-dio-48e: Make irq_chip immutable

Kernel warns about mutable irq_chips:

    "not an immutable chip, please consider fixing!"

Make the struct irq_chip const, flag it as IRQCHIP_IMMUTABLE, add the
new helper functions, and call the appropriate gpiolib functions.
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

drivers/gpio/gpio-104-dio-48e.c

@@ -164,6 +164,7 @@ static void dio48e_irq_mask(struct irq_data *data)
 		dio48egpio->irq_mask &= ~BIT(0);
 	else
 		dio48egpio->irq_mask &= ~BIT(1);
+	gpiochip_disable_irq(chip, offset);
 
 	if (!dio48egpio->irq_mask)
 		/* disable interrupts */
@@ -191,6 +192,7 @@ static void dio48e_irq_unmask(struct irq_data *data)
 		iowrite8(0x00, &dio48egpio->reg->enable_interrupt);
 	}
 
+	gpiochip_enable_irq(chip, offset);
 	if (offset == 19)
 		dio48egpio->irq_mask |= BIT(0);
 	else
@@ -213,12 +215,14 @@ static int dio48e_irq_set_type(struct irq_data *data, unsigned int flow_type)
 	return 0;
 }
 
-static struct irq_chip dio48e_irqchip = {
+static const struct irq_chip dio48e_irqchip = {
 	.name = "104-dio-48e",
 	.irq_ack = dio48e_irq_ack,
 	.irq_mask = dio48e_irq_mask,
 	.irq_unmask = dio48e_irq_unmask,
-	.irq_set_type = dio48e_irq_set_type
+	.irq_set_type = dio48e_irq_set_type,
+	.flags = IRQCHIP_IMMUTABLE,
+	GPIOCHIP_IRQ_RESOURCE_HELPERS,
 };
 
 static irqreturn_t dio48e_irq_handler(int irq, void *dev_id)
@@ -322,7 +326,7 @@ static int dio48e_probe(struct device *dev, unsigned int id)
 	dio48egpio->chip.set_multiple = dio48e_gpio_set_multiple;
 
 	girq = &dio48egpio->chip.irq;
-	girq->chip = &dio48e_irqchip;
+	gpio_irq_chip_set_chip(girq, &dio48e_irqchip);
 	/* This will let us handle the parent IRQ in the driver */
 	girq->parent_handler = NULL;
 	girq->num_parents = 0;