staging: most: hdm-usb: fix mbo buffer leak

This patch fixes an MBO leak by replacing the proprietary
free_anchored_buffers() function with the usb_kill_anchored_urbs() function
of the USB subsystem and guarantees that the mbo->complete() completion
function is being called for each URB.

Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>