drm/amd/powerplay: fix the incorrect type of pptable

This patch is to fix the incorrect type of pptable, otherwise, the data will be
totally wrong in parsing phase.

Signed-off-by: Kenneth Feng <Kenneth.Feng@amd.com>
Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>