drm/amd/display: Don't trigger flip twice when ODM combine in use

[Why]
When ODM combine is in use we trigger multiple update events causing
issues with variable refresh rate.

[How]
Only trigger on a single ODM instance.

Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>