staging: most: hdm-usb: remove calls to usb_unachor_urb

This patch removes the calls to usb_unanchor_urb() from the completion
routines, since disassociation of the URBs is already handles by the
USB subsystem.

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