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.