iio: adc: rtq6056: Correct the sign bit index

[ Upstream commit 9b45744 ]

The vshunt/current reported register is a signed 16bit integer. The
sign bit index should be '15', not '16'.

Fixes: 4396f45 ("iio: adc: Add rtq6056 support")
Reported-by: Andy Hsu <andy_ya_hsu@wiwynn.com>
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
[ adapted switch statement to existing if-else structure for sign_extend32() fix ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ChiYuan Huang

drivers/iio/adc/rtq6056.c

@@ -171,7 +171,7 @@ static int rtq6056_adc_read_channel(struct rtq6056_priv *priv,
 	if (addr == RTQ6056_REG_BUSVOLT || addr == RTQ6056_REG_POWER)
 		*val = regval;
 	else
-		*val = sign_extend32(regval, 16);
+		*val = sign_extend32(regval, 15);
 
 	return IIO_VAL_INT;
 }