drm/amd/display: Fix dc_sink kref count in emulated_link_detect

[why]
prev_sink is not used anywhere else in the function and the reference to
it from dc_link is replaced with a new dc_sink.

[how]
Change dc_sink_retain(prev_sink) to dc_sink_release(prev_sink).

Signed-off-by: Victor Lu <victorchengchi.lu@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -1833,8 +1833,8 @@ static void emulated_link_detect(struct dc_link *link)
 	link->type = dc_connection_none;
 	prev_sink = link->local_sink;
 
-	if (prev_sink != NULL)
-		dc_sink_retain(prev_sink);
+	if (prev_sink)
+		dc_sink_release(prev_sink);
 
 	switch (link->connector_signal) {
 	case SIGNAL_TYPE_HDMI_TYPE_A: {