lavapipe: check all vertex-stages

lavapipe: check all vertex-stages

We should really check for the minimum of all supported vertex-stages
here, not just the vertex-shader.

This shouldn't make any real-world difference, because we really only
support LLVMpipe here, and that driver has the same limits for all
stages. But it seems better to actually check all stages instead of just
assuming.

Fixes: b38879f8c5f ("vallium: initial import of the vulkan frontend")
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10189>