MAINTAINERS: Add missing ASoC OMAP co-maintainer

Peter Ujfalusi has been co-maintaining sound/soc/omap/ for years but
was missing from this MAINTAINERS entry.

Signed-off-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>