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 void chmod_sysfs_attrs(struct hid_device *hdev)
{
	struct attribute **attr;
	u8 buf[2];
	int ret;

	ret = cp2112_hid_get(hdev, CP2112_LOCK_BYTE, buf, sizeof(buf),
			     HID_FEATURE_REPORT);
	if (ret != sizeof(buf)) {
		hid_err(hdev, "error reading lock byte: %d\n", ret);
		return;
	}

	for (attr = cp2112_attr_group.attrs; *attr; ++attr) {
		umode_t mode = (buf[1] & 1) ? S_IWUSR | S_IRUGO : S_IRUGO;
		ret = sysfs_chmod_file(&hdev->dev.kobj, *attr, mode);
		if (ret < 0)
			hid_err(hdev, "error chmoding sysfs file %s\n",
				(*attr)->name);
		buf[1] >>= 1;
	}
}

static void chmod_sysfs_attrs(struct hid_device *hdev)
{
	struct attribute **attr;
	u8 buf[2];
	int ret;

	ret = cp2112_hid_get(hdev, CP2112_LOCK_BYTE, buf, sizeof(buf),
			     HID_FEATURE_REPORT);
	if (ret != sizeof(buf)) {
		hid_err(hdev, "error reading lock byte: %d\n", ret);
		return;
	}

	for (attr = cp2112_attr_group.attrs; *attr; ++attr) {
		umode_t mode = (buf[1] & 1) ? S_IWUSR | S_IRUGO : S_IRUGO;
		ret = sysfs_chmod_file(&hdev->dev.kobj, *attr, mode);
		if (ret < 0)
			hid_err(hdev, "error chmoding sysfs file %s\n",
				(*attr)->name);
		buf[1] >>= 1;
	}
}
