ASoC: core: Fix check before defaulting to regmap

Check if the chip has provided a write operation (which is mandatory for
I/O) rather than looking for control data as some of the MFDs use a global
for this. Also skip the attempt if there's no regmap available by device
in case things get confused by the attempt to default.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Tested-by: Peter Ujfalusi <peter.ujfalusi@ti.com>