HID: cp2112: fix gpio-callback error handling

In case of a zero-length report, the gpio direction_input callback would
currently return success instead of an errno.

Fixes: 1ffb3c40 ("HID: cp2112: make transfer buffers DMA capable")
Cc: stable <stable@vger.kernel.org>     # 4.9
Signed-off-by: NJohan Hovold <johan@kernel.org>
Reviewed-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/hid-cp2112.c

@@ -213,7 +213,7 @@ static int cp2112_gpio_direction_input(struct gpio_chip *chip, unsigned offset)
 
 exit:
 	mutex_unlock(&dev->lock);
-	return ret <= 0 ? ret : -EIO;
+	return ret < 0 ? ret : -EIO;
 }
 
 static void cp2112_gpio_set(struct gpio_chip *chip, unsigned offset, int value)