HID: i2c-hid: fix return paths

Forwards appropriate return values.
As noone use the error returned by i2c_hid_get_input, let's make it
returning void.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Reviewed-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>