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

In the Linux kernel, the following vulnerability has been resolved: 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. (cherry picked from commit 45510cf662dcf46b5d8926d454f338809f107b9d)