radv: fix shared memory load/stores.

radv: fix shared memory load/stores.

If we have an indirect index here we need to scale it by attribute slots
e.g. is this is vec2[256] then we get an indir_index in the 0.255 range
but the vec2 are aligned inside vec4 slots. So scale the indir index,
then extract the channels.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Cc: "17.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>