ASoC: Optimise WM9081 FLL performance

Tune the FLL gain for optimal performance according to evaluation
results.

Signed-off-by: Mario Becroft <mb@gem.win.co.nz>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>