drm/amd/display: Ensure commit_streams returns the DC return code

[Description]
- Ensure dc_commit_streams returns the correct return code so any
  failures can be handled properly in DM layer
- If set timings fail and we have to remove MPO planes, do so
  unconditionally but make sure to mark for removal so we report
  the VSYNC and prevent timeout
- Failure to remove MPO plane results in set timings failure due
  to lack of resources

Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Stylon Wang <stylon.wang@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>

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -1988,7 +1988,7 @@ context_alloc_fail:
 
 	DC_LOG_DC("%s Finished.\n", __func__);
 
-	return (res == DC_OK);
+	return res;
 }
 
 /* TODO: When the transition to the new commit sequence is done, remove this