Currently when the HWC creation fails, the error handling is flawed,
e.g. if mana_hwc_create_channel() -> mana_hwc_establish_channel() fails,
the resources acquired in mana_hwc_init_queues() is not released.

Enhance mana_hwc_destroy_channel() to do the proper cleanup work and
call it accordingly.

MFC after:	2 weeks
Sponsored by:	Microsoft