ASoC: atmel: Fixes for AT91SAM9G20-EK audio driver

Merge series from Mark Brown <broonie@kernel.org>:

At some point the machine driver for the audio subsystem on the
AT91SAM9G20-EK appears to have bitrotted, no longer probing due to
effects of the transition to the common clock framework. The first patch
in this series fixes the initial probe problem, with the rest of the
series being random other fixes and cleanups I noticed while looking at
the driver.