ASoC: wm8400: Fix setting Fout clock divider for FLL Control 4

What we want here is to clear the WM8400_FLL_OUTDIV_MASK bits then
OR with factors.outdiv.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>