drm/amd/display: Add null check in resource_log_pipe_topology_update

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Add null check in resource_log_pipe_topology_update [WHY] When switching from "Extend" to "Second Display Only" we sometimes call resource_get_otg_master_for_stream on a stream for the eDP, which is disconnected. This leads to a null pointer dereference. [HOW] Added a null check in dc_resource.c/resource_log_pipe_topology_update.