gpio: 104-idi-48: Fix missing spin_lock_init for ack_lock

Fixes: 9ae482104c ("gpio: 104-idi-48: Clear pending interrupt once in IRQ handler")
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-104-idi-48.c

@@ -247,6 +247,7 @@ static int idi_48_probe(struct device *dev, unsigned int id)
 	idi48gpio->irq = irq[id];
 
 	spin_lock_init(&idi48gpio->lock);
+	spin_lock_init(&idi48gpio->ack_lock);
 
 	dev_set_drvdata(dev, idi48gpio);