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: 1ffb3c40ffb5 ("HID: cp2112: make transfer buffers DMA capable")
Cc: stable <stable@vger.kernel.org>     # 4.9
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
static int cp2112_hid_output(struct hid_device *hdev, u8 *data, size_t count,
			     unsigned char report_type)
{
	u8 *buf;
	int ret;

	buf = kmemdup(data, count, GFP_KERNEL);
	if (!buf)
		return -ENOMEM;

	if (report_type == HID_OUTPUT_REPORT)
		ret = hid_hw_output_report(hdev, buf, count);
	else
		ret = hid_hw_raw_request(hdev, buf[0], buf, count, report_type,
				HID_REQ_SET_REPORT);

	kfree(buf);
	return ret;
}

static int cp2112_hid_output(struct hid_device *hdev, u8 *data, size_t count,
			     unsigned char report_type)
{
	u8 *buf;
	int ret;

	buf = kmemdup(data, count, GFP_KERNEL);
	if (!buf)
		return -ENOMEM;

	if (report_type == HID_OUTPUT_REPORT)
		ret = hid_hw_output_report(hdev, buf, count);
	else
		ret = hid_hw_raw_request(hdev, buf[0], buf, count, report_type,
				HID_REQ_SET_REPORT);

	kfree(buf);
	return ret;
}
