Overlay plugins got broken because ovl_offset.pl assumes the audio buffer
ends where the plugin buffer starts. Buflib however keeps its handle table
there, so there are a few hundred bytes fewer available, so loading the
overlay fails. We work around this by linking the overlay at a slightly
lower address (1024 bytes lower). If the handle table ever grows more than
that, overlays will start failing again and we either need a different
solution or increase the margin a bit.
Change-Id: Id98cb52da2c8c4a4bc773362a46f646774112f85
