drm/amd/display: detect_link_and_local_sink: DP alt mode timeout path leaks prev_sink...

drm/amd/display: detect_link_and_local_sink: DP alt mode timeout path leaks prev_sink reference

prev_sink is unconditionally retained via dc_sink_retain at function
  entry, but the DP alt mode timeout path inside SIGNAL_TYPE_DISPLAY_PORT
  returns false without releasing prev_sink. All other return paths in the
  function correctly call dc_sink_release(prev_sink), making this the only
  missing cleanup.

Fixes: 54618888d1ea ("drm/amd/display: break down dc_link.c")
Signed-off-by: WenTao Liang <vulab@iscas.ac.cn>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Link: https://patch.msgid.link/20260626124555.36910-1-vulab@iscas.ac.cn
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 45510cf662dcf46b5d8926d454f338809f107b9d)
Cc: stable@vger.kernel.org