drm/amd/powerplay: issue no PPSMC_MSG_GetCurrPkgPwr on unsupported ASICs

Otherwise, the error message prompted will confuse user.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>