Input: ads7846 - fix device usage within attribute show

With commit e585c40 (Input: ads7846 - convert to
hwmon_device_register_with_groups()) the device passed to the attribute's
show function isn't the spi device as before.
So fixup the passed device to ads7846_read12_ser.

Signed-off-by: Alexander Stein <alexanders83@web.de>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/ads7846.c

@@ -425,7 +425,7 @@ static int ads7845_read12_ser(struct device *dev, unsigned command)
 name ## _show(struct device *dev, struct device_attribute *attr, char *buf) \
 { \
 	struct ads7846 *ts = dev_get_drvdata(dev); \
-	ssize_t v = ads7846_read12_ser(dev, \
+	ssize_t v = ads7846_read12_ser(&ts->spi->dev, \
 			READ_12BIT_SER(var)); \
 	if (v < 0) \
 		return v; \