drm/amd/display: Fix black flash when switching from ODM2to1 to ODMBypass

[Why]
On secondary display hotplug we switch primary
stream from ODM2to1 to ODMBypass mode. Current
logic will trigger disabling front end for this
stream.

[How]
We need to check if prev_odm_pipe is equal to NULL
in order to disable dangling planes in this scenario.

Reviewed-by: Ariel Bernstein <Eric.Bernstein@amd.com>
Acked-by: Brian Chang <Brian.Chang@amd.com>
Signed-off-by: Vladimir Stempen <vladimir.stempen@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

@@ -1094,7 +1094,8 @@ static void disable_dangling_plane(struct dc *dc, struct dc_state *context)
 				dc->current_state->stream_count != context->stream_count)
 			should_disable = true;
 
-		if (old_stream && !dc->current_state->res_ctx.pipe_ctx[i].top_pipe) {
+		if (old_stream && !dc->current_state->res_ctx.pipe_ctx[i].top_pipe &&
+				!dc->current_state->res_ctx.pipe_ctx[i].prev_odm_pipe) {
 			struct pipe_ctx *old_pipe, *new_pipe;
 
 			old_pipe = &dc->current_state->res_ctx.pipe_ctx[i];