drm/amd/display: Break after finding supported vlevel for repopulate

[Description]
After repopulating pipes for a split / merge, we want to find the
lowest vlevel that supports the desired mpc combine level.

Reviewed-by: Nevenko Stupar <nevenko.stupar@amd.com>
Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>