MAINTAINERS: change the Atmel audio alsa driver entry

I take over the the maintainship of Atmel alsa drivers from Voice.
Thanks for your work!

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>