Input: ad7879 - return plain error code from ad7879_probe()

With the switch to devm, there is no need for ad7879_probe() to return the
touchscreen structure, we can use plain error code. This also fixes issue
introduced with devm concersion, where we returned 0 on success (which
worked OK since IS_ERR(0) would not trigger, but was not correct
regardless).

Fixes: 381f688eee3d ("Input: ad7879 - use more devm interfaces")
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/ad7879.h

@@ -11,13 +11,12 @@
 
 #include <linux/types.h>
 
-struct ad7879;
 struct device;
 struct regmap;
 
 extern const struct dev_pm_ops ad7879_pm_ops;
 
-struct ad7879 *ad7879_probe(struct device *dev, struct regmap *regmap,
-			    int irq, u16 bustype, u8 devid);
+int ad7879_probe(struct device *dev, struct regmap *regmap,
+		 int irq, u16 bustype, u8 devid);
 
 #endif