gpio: mt7621: support gpio-line-names property

This driver uses multiple gpiochip banks per device. To support
'gpio-line-names' along the banks 'offset' for each bank must be
set explicitly.
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpio-mt7621.c

@@ -241,6 +241,7 @@ mediatek_gpio_bank_probe(struct device *dev,
 	if (!rg->chip.label)
 		return -ENOMEM;
 
+	rg->chip.offset = bank * MTK_BANK_WIDTH;
 	rg->irq_chip.name = dev_name(dev);
 	rg->irq_chip.parent_device = dev;
 	rg->irq_chip.irq_unmask = mediatek_gpio_irq_unmask;