drm/amd/pm: avoid driver getting empty metrics table for the first time

add metrics.AccumulationCouter check to avoid driver getting an empty
metrics data since metrics table not updated completely in pmfw side.

Signed-off-by: Yang Wang <KevinYang.Wang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Tested-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>