drm/amd/display: Remove always true condition

[WHAT & HOW]
advanced_pstate_switching was initialized to false and never assigned to
another value; as a result !advanced_pstate_switching is always true and
should be removed.

This fixes 2 DEADCODE issues reported by Coverity.

Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>