drm/amdgpu: adjust fw_name string length for toc

Adjust toc fw_name string length to PSP_FW_NAME_LEN.

Signed-off-by: Lang Yu <lang.yu@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>