intel/compiler: fix array & struct IO lowering in mesh shaders

intel/compiler: fix array & struct IO lowering in mesh shaders

We really need offsets to be in dwords, not in vec4s.

The bug manifests as random failure of func.mesh.clipdistance.5 crucible
test, where stores to gl_MeshVerticesNV[x].gl_ClipDistance[4+n] actually write to
gl_MeshVerticesNV[x].gl_ClipDistance[1+n].

Fixes: 1f438eb0337 ("intel/compiler: Implement Mesh Output")
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14997>