drm/amd/display: Don't pass invalid fw_bss_data pointer into DMUB srv

[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: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Zhan Liu <Zhan.Liu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -1228,10 +1228,10 @@ static int dm_dmub_sw_init(struct amdgpu_device *adev)
 					PSP_HEADER_BYTES - PSP_FOOTER_BYTES;
 	region_params.bss_data_size = le32_to_cpu(hdr->bss_data_bytes);
 	region_params.vbios_size = adev->bios_size;
-	region_params.fw_bss_data =
+	region_params.fw_bss_data = region_params.bss_data_size ?
 		adev->dm.dmub_fw->data +
 		le32_to_cpu(hdr->header.ucode_array_offset_bytes) +
-		le32_to_cpu(hdr->inst_const_bytes);
+		le32_to_cpu(hdr->inst_const_bytes) : NULL;
 	region_params.fw_inst_const =
 		adev->dm.dmub_fw->data +
 		le32_to_cpu(hdr->header.ucode_array_offset_bytes) +