drm/amd/pm: correct the ACPI table setup V2

Correct the setting for "ActivityLevel".

V2: rich the comment

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>