drm/amd/display: drop duplicated .dsc_pg_control for dcn30

There're 2 .dsc_pg_control, drop the first one.
	.dsc_pg_control = NULL,
	.dsc_pg_control = dcn20_dsc_pg_control,

Signed-off-by: Flora Cui <flora.cui@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>