drm/amd/display: Fix visual confirm bug for SubVP

[Why]
Visual confirm was incorrect on dual monitor SubVP setup

[How]
Adjusted p_state assignment for dual monitor SubVP setup

Signed-off-by: Ryan Seto <ryanseto@amd.com>
Reviewed-by: Chaitanya Dhere <chaitanya.dhere@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>