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].