ASoC: AC97 doesn't use regmap by default

Since commit 38cbf959
("ASoC: core: Try to use regmap if the driver doesn't set up any I/O")
any ASoC codec which doesn't set codec::control_data is assumed
to use regmap.  That doesn't work with AC97 so this workaround
sets the codec::control_data member to a random value to restore
proper behaviour.

Tested with WM9712.

Signed-off-by: Manuel Lauss <manuel.lauss@googlemail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>