ASoC: wm8974: set cache type for regmap

ASoC: wm8974: set cache type for regmap

commit 1ea5998afe903384ddc16391d4c023cd4c867bea upstream.

Attempting to use this codec driver triggers a BUG() in regcache_sync()
since no cache type is set.  The register map of this device is fairly
small and has few holes so a flat cache is suitable.

Signed-off-by: Mans Rullgard <mans@mansr.com>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>