drm/amd/display: Fix Synaptics Cascaded Panamera DSC Determination

Synaptics Cascaded Panamera topology needs to unconditionally
acquire root aux for dsc decoding.

Reviewed-by: Roman Li <roman.li@amd.com>
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>