[Why]
If bss_data_size is 0 then we shouldn't be passing down fw_bss_data into
the DMUB service since the region isn't really "valid."

[How]
Pass NULL instead if the size is 0.
Signed-off-by: NNicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: NZhan Liu <Zhan.Liu@amd.com>
Acked-by: NRodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>