staging: usbip: Fix build on Debian ppc

One missing include was added.

Signed-off-by: Dominik Paulus <dominik.paulus@fau.de>
Signed-off-by: Tobias Polzer <tobias.polzer@fau.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>