drm/amdgpu: Avoid fetching VRAM vendor info

The present way to fetch VRAM vendor information turns out to be not
reliable on GFX 9.4.3 dGPUs as well. Avoid using the data.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org