ASoC: sta32x: Move regulator acquisition to I2C probe

This is better style as it ensures we don't try to do the ASoC probe
without required resources. Also convert to devm_ while we're at it,
saving a bit of code, and fix a leak of enable on error.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Johannes Stezenbach <js@sig21.net>