ASoC: arizona: Calculate FLL gain last

No part of the FLL calculation depends on the value determined for the
gain but the gain does depend on other values. In preparation for future
updates this patch moves the gain to be the last thing calculated.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>