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

Fixes: 9ae482104cb9 ("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>
diff --git a/drivers/gpio/gpio-104-idi-48.c b/drivers/gpio/gpio-104-idi-48.c
index 6c75c83..2d2763e 100644
--- a/drivers/gpio/gpio-104-idi-48.c
+++ b/drivers/gpio/gpio-104-idi-48.c
@@ -247,6 +247,7 @@
 	idi48gpio->irq = irq[id];
 
 	spin_lock_init(&idi48gpio->lock);
+	spin_lock_init(&idi48gpio->ack_lock);
 
 	dev_set_drvdata(dev, idi48gpio);