usb: usbip: fix usbip.h path in userspace tool

Fixes: 588b48ca ("usbip: move usbip userspace code out of staging")
which introduced build failure by not changing uapi/usbip.h include path
according to new location.

Signed-off-by: Piotr Król <piotr.krol@3mdeb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>