rt2x00usb: check USB's request error code in rt2800usb_autorun_detect()

rt2800usb_autorun_detect() blindly assumes assumes that it worked while
it could have failed. Check the error code here.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/rt2x00/rt2800usb.c

@@ -233,6 +233,7 @@ static int rt2800usb_autorun_detect(struct rt2x00_dev *rt2x00dev)
 {
 	__le32 *reg;
 	u32 fw_mode;
+	int ret;
 
 	reg = kmalloc(sizeof(*reg), GFP_KERNEL);
 	if (reg == NULL)
@@ -242,11 +243,14 @@ static int rt2800usb_autorun_detect(struct rt2x00_dev *rt2x00dev)
 	 * magic value USB_MODE_AUTORUN (0x11) to the device, thus the
 	 * returned value would be invalid.
 	 */
-	rt2x00usb_vendor_request(rt2x00dev, USB_DEVICE_MODE,
-				 USB_VENDOR_REQUEST_IN, 0, USB_MODE_AUTORUN,
-				 reg, sizeof(*reg), REGISTER_TIMEOUT_FIRMWARE);
+	ret = rt2x00usb_vendor_request(rt2x00dev, USB_DEVICE_MODE,
+				       USB_VENDOR_REQUEST_IN, 0,
+				       USB_MODE_AUTORUN, reg, sizeof(*reg),
+				       REGISTER_TIMEOUT_FIRMWARE);
 	fw_mode = le32_to_cpu(*reg);
 	kfree(reg);
+	if (ret < 0)
+		return ret;
 
 	if ((fw_mode & 0x00000003) == 2)
 		return 1;