drm/amd/display: Handle the case which quad_part is equal 0

Add code to handle case when quad_part is 0 in gpu_addr_to_uma().

Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>