ASoC: ad193x: tweak style to match other codecs

Rename the snd_soc_control_type field from "bus_type" to "control_type",
and drop the now unused "control_data" field.

Signed-off-by: Scott Jiang <scott.jiang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>