drm/amd/display: Clean Up VPG Low Mem Power

[WHAT]
One of the current VPG power on calls is unnecessary

Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Agustin Gutierrez Sanchez <agustin.gutierrez@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>