staging: most: hdm-usb: make use of is_channel_healthy flag

This patch makes the write completion handler use the is_channel_healthy
flag to prevent the hdm from scheduling a second clear_halt workqueue in
case an endpoint reported a STALL condition.

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