drm/amd/display: Skip plane when not found by stream id

[Why & How]
dml_stream_idx will be -1 when it is not found. Check and skip in such a
case as -1 is not a valid array index.

This fixes a NEGATIVE_RETURNS issue reported by Coverity.
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@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>

drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_utils.c

@@ -465,7 +465,10 @@ void dml21_build_fams2_programming(const struct dc *dc,
 		}
 
 		dml_stream_idx = dml21_helper_find_dml_pipe_idx_by_stream_id(dml_ctx, stream->stream_id);
-		ASSERT(dml_stream_idx >= 0);
+		if (dml_stream_idx < 0) {
+			ASSERT(dml_stream_idx >= 0);
+			continue;
+		}
 
 		/* copy static state from PMO */
 		memcpy(static_state,