staging: most: hdm-usb: remove proprietary urb anchoring

This patch removes the propietary tracking of URBs. Instead the structure
usb_anchor of the USB subsystem is used.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>