mfd: arizona: Correct register definition for FLL2_SYNC_BW

We had specified the mask twice for FLL2_SYNC_BW change the first mask
definition in a bit definition to match the other fields.

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