usbip: Add USB_SPEED_SUPER as valid arg

With this patch, USB_SPEED_SUPER is a valid speed when attaching
a USB3 SuperSpeed device.

Signed-off-by: Yuyang Du <yuyang.du@intel.com>
Acked-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>