staging: usbip: reformat function stub_recv_cmd_unlink()

Reformat function stub_recv_cmd_unlink() to improve readability.

Signed-off-by: Kurt Kanzenbach <ly80toro@cip.cs.fau.de>
Signed-off-by: Stefan Reif <ke42caxa@cip.cs.fau.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>