drm/amd/display: Fix various issues found by compiler warning as errors

[Why]
Diagnostics team reported various issues found when enabling warnings as errors

[How]
Fix implicit conversions

Signed-off-by: Eric Bernstein <eric.bernstein@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>