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.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Tested-by: Mark Broadworth <mark.broadworth@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>