drm/amdgpu: Remove check which is not valid for certain VBIOS

commit ab6613b7eaefe85dadfc86025e901c55d71c0379 upstream.

Fixes vbios fetching on certain headless boards.

Signed-off-by: Ken Wang <Ken.Wang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>