codec->control_data has to be left unset to make the ASoC core access
the regmap properly.

That bug slipped in during a rebase session of the driver refactoring.
Signed-off-by: NDaniel Mack <zonque@gmail.com>
Acked-by: NLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: NMark Brown <broonie@linaro.org>