staging: usbip: remove double giveback of URB

In the vhci_urb_dequeue() function the TCP connection is checked twice.
Each time when the TCP connection is closed the URB is unlinked and given
back. Remove the second attempt of unlinking and giving back of the URB completely.

This patch fixes the bug described at https://bugzilla.kernel.org/show_bug.cgi?id=24872 .

Signed-off-by: Márton Németh <nm127@freemail.hu>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>