zink: fix caching of shader variants with inlined uniforms

zink: fix caching of shader variants with inlined uniforms

attempting to read the inlined uniforms directly after the variant key
using the size of the variant is not going to work since the variant union
is (sometimes) much larger than the size of the actual struct being used,
meaning that this would just copy a bunch of zeroes instead of the actual
inlined uniforms

Fixes: 7f28775edcc ("zink: implement uniform inlining")

Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11003>