ASoC: Fix incorrect parameter to snd_soc_codec_volatile_register

We need to pass the register index and not the register value.
This patch depends on my previous patch "ASoC: Delegate to hw
specific read for volatile registers".

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>