gpio: xilinx: Fix bug where the wrong GPIO register is written to

Care is taken with "index", however with the current version
the actual xgpio_writereg is using index for data but
xgpio_regoffset(chip, i) for the offset. And since i is already
incremented it is incorrect. This patch fixes it so that index
is used for the offset too.

Cc: stable@vger.kernel.org
Signed-off-by: Paul Thomas <pthomas8589@gmail.com>
Link: https://lore.kernel.org/r/20200125221410.8022-1-pthomas8589@gmail.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-xilinx.c

@@ -147,9 +147,10 @@ static void xgpio_set_multiple(struct gpio_chip *gc, unsigned long *mask,
 	for (i = 0; i < gc->ngpio; i++) {
 		if (*mask == 0)
 			break;
+		/* Once finished with an index write it out to the register */
 		if (index !=  xgpio_index(chip, i)) {
 			xgpio_writereg(chip->regs + XGPIO_DATA_OFFSET +
-				       xgpio_regoffset(chip, i),
+				       index * XGPIO_CHANNEL_OFFSET,
 				       chip->gpio_state[index]);
 			spin_unlock_irqrestore(&chip->gpio_lock[index], flags);
 			index =  xgpio_index(chip, i);
@@ -165,7 +166,7 @@ static void xgpio_set_multiple(struct gpio_chip *gc, unsigned long *mask,
 	}
 
 	xgpio_writereg(chip->regs + XGPIO_DATA_OFFSET +
-		       xgpio_regoffset(chip, i), chip->gpio_state[index]);
+		       index * XGPIO_CHANNEL_OFFSET, chip->gpio_state[index]);
 
 	spin_unlock_irqrestore(&chip->gpio_lock[index], flags);
 }