drm/amd/display: fix multi-display on CZ

- fixed wrong index in dce110_validate_surface_sets()
- formatted for better readability

Signed-off-by: Roman Li <Roman.Li@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
igned-off-by: Alex Deucher <alexander.deucher@amd.com>