Xworld - Fixes warnings for cowond2, hifimanhm60x, ibassodx50, and
ondavx747.  Also fixes errors for ondavx777.

Change-Id: I1a5daa844759316df4dec7b869425ea9a174814b
Reviewed-on: http://gerrit.rockbox.org/1081
Reviewed-by: Marcin Bukat <marcin.bukat@gmail.com>