staging: rtl8712: add error handler in r8712_usbctrl_vendorreq()

When 'status' returned from usb_control_msg() is not equal to 'len',
that usb_control_msg() is on partial failure, r8712_usbctrl_vendorreq()
will treat partial reads as success.

Reviewed-by: Dan Carpenter <[e-mail]>
Signed-off-by: Wang Cheng <[e-mail]>
Link: https://lore.kernel.org/r/e33[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/rtl8712/usb_ops_linux.c

···
 	}
 	status = usb_control_msg(udev, pipe, request, reqtype, value, index,
 				 pIo_buf, len, 500);
-	if (status > 0) {  /* Success this control transfer. */
-		if (requesttype == 0x01) {
-			/* For Control read transfer, we have to copy the read
-			 * data from pIo_buf to pdata.
-			 */
-			memcpy(pdata, pIo_buf,  status);
-		}
+	if (status < 0)
+		goto free;
+	if (status != len) {
+		status = -EREMOTEIO;
+		goto free;
 	}
+	/* Success this control transfer. */
+	if (requesttype == 0x01) {
+		/* For Control read transfer, we have to copy the read
+		 * data from pIo_buf to pdata.
+		 */
+		memcpy(pdata, pIo_buf, status);
+	}
+
+free:
 	kfree(palloc_buf);
 	return status;
 }