drm/amd/display: Match expected data types

drm/amd/display: Match expected data types

[Why/How]
Data types should match what is expected.
Update/cast data accordingly.

Also change ASSERT to use DML_ASSERT instead

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Zheng Austin <Austin.Zheng@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>