usbip: Fix vhci_urb_enqueue() URB null transfer buffer error path

Fix vhci_urb_enqueue() to print debug msg and return error instead of
failing with BUG_ON.
Signed-off-by: Shuah Khan <shuah@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/usbip/vhci_hcd.c

@@ -702,8 +702,10 @@ static int vhci_urb_enqueue(struct usb_hcd *hcd, struct urb *urb, gfp_t mem_flag
 	}
 	vdev = &vhci_hcd->vdev[portnum-1];
 
-	/* patch to usb_sg_init() is in 2.5.60 */
-	BUG_ON(!urb->transfer_buffer && urb->transfer_buffer_length);
+	if (!urb->transfer_buffer && urb->transfer_buffer_length) {
+		dev_dbg(dev, "Null URB transfer buffer\n");
+		return -EINVAL;
+	}
 
 	spin_lock_irqsave(&vhci->lock, flags);