usbip: vhci_hcd: at unlink, return -EIDRM if vhci_rx took the urb

In a situation where the urb is about to be returned or was never
there, we should return -EIDRM (as per usb_hcd_check_unlink_urb).
This is exactly the situation when the urb is picked up by vhci_rx
before we access priv.

Return -EIDRM rather than 0 when this happens.

Signed-off-by: Igor Kotrasinski <i.kotrasinsk@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>