drm/amd/display: Resolve Coverity Issues

[WHY]
Remove coverity issues that were originally ignored.

[HOW]
Ran coverity locally on driver, used output report to find existing
coverity issues, resolved them

Reviewed-by: Nicholas Choi <nicholas.choi@amd.com>
Signed-off-by: Daniel Sa <Daniel.Sa@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>