No need to reset the wptr and clear the rings.  The UNMAP_QUEUES
packet writes the current MQD state back the MQD on suspend,
so there is no need to reset it as well.

v2: fix from gfx8 (Rex)
Acked-by: Tom St Denis <tom.stdenis@amd.com>
Acked-by: monk liu <monk.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>