ASoC: Fix incorrect register cache size configuration

The reg_cache_size is the number of elements in the register cache,
not the size of the cache itself. This is not a problem if the size
of each element of the cache is 1 byte but it matters in any other
case.

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>