mfd: arizona: Remove BUG_ON usage

BUG_ON macros are generally frowned upon when the issue isn't super
critical, the kernel can certainly carry on with the 32k clock on the
CODEC in a bad state so change the BUG_ON to a WARN_ON.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>