mfd: Fix off by one in WM831x IRQ code

The GPIO IRQs aren't the first IRQs defined, we need to subtract the base
for the GPIOs as well to use them for array indexes.

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/wm831x-irq.c

@@ -408,6 +408,11 @@ static int wm831x_irq_set_type(struct irq_data *data, unsigned int type)
 			return -EINVAL;
 	}
 
+	/* Rebase the IRQ into the GPIO range so we've got a sensible array
+	 * index.
+	 */
+	irq -= WM831X_IRQ_GPIO_1;
+
 	/* We set the high bit to flag that we need an update; don't
 	 * do the update here as we can be called with the bus lock
 	 * held.