Apparently this doesn't always work reliably, e.g. at resume time.

Just initialize to 0, so the ring is considered empty.

Tested with hibernation on Sumo and Cayman cards.

Should fix https://bugs.launchpad.net/ubuntu/+source/linux/+bug/820746/ .
Signed-off-by: NMichel Dänzer <michel.daenzer@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
cc: stable@kernel.org
Signed-off-by: NDave Airlie <airlied@redhat.com>