gallivm: (trivial) handle non-aligned fetch for lp_build_fetch_rgba_soa

gallivm: (trivial) handle non-aligned fetch for lp_build_fetch_rgba_soa

soa fetch so far always assumed that data was aligned. However, we want to
use this for vertex fetch, and data might not be aligned there, so handle
it in this path too (basically just pass through alignment through to other
functions). (It looks like it wouldn't work for for cached s3tc but this is
no different than with AoS fetch.)

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>