drm/amd/display: Don't treat wb connector as physical in create_validate_stream_for_sink

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Don't treat wb connector as physical in create_validate_stream_for_sink Don't try to operate on a drm_wb_connector as an amdgpu_dm_connector. While dereferencing aconnector->base will "work" it's wrong and might lead to unknown bad things. Just... don't.