drm/amd/display: Remove useless comparison of unsigned int vs. 0

drm/amd/display: Remove useless comparison of unsigned int vs. 0

[WHY & HOW]
The comparisons of unsigned int with 0 can have no meanings, i.e.
unsigned int >= 0 (always true) or unsigned int < 0 (always false), and
therefore they are removed.

This fixes 12 NO_EFFECT issues reported by Coverity.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>