drm/amd/display: Fix p-state type when p-state is unsupported

drm/amd/display: Fix p-state type when p-state is unsupported

[WHY&HOW]
P-state type would remain on previously used when unsupported which
causes confusion in logging and visual confirm, so set back to zero
when unsupported.

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Dillon Varone <Dillon.Varone@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>