drm/amd/display: Avoid divide by zero by initializing dummy pitch to 1

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Avoid divide by zero by initializing dummy pitch to 1 [Why] If the dummy values in `populate_dummy_dml_surface_cfg()` aren't updated then they can lead to a divide by zero in downstream callers like CalculateVMAndRowBytes() [How] Initialize dummy value to a value to avoid divide by zero.