drm/amdgpu/atomfirmware: fix vram_info fetching for renoir

Renoir uses integrated_system_info table v12.  The table
has the same layout as v11 with respect to this data.  Just
reuse the existing code for v12 for stable.

Fixes incorrectly reported vram info in the driver output.

Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org