staging: most: hdm-usb: fix clear halt processing

This patch is needed to ensure that submitted URBs get unlinked before
the driver calls usb_clear_halt(). Since the halt condition of an USB
endpoint is channel related, the work_struct is moved from a buffer
basis to a channel basis.

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