ASoC: wm8940: Fix setting PLL Output clock division ratio

According to the datasheet:
The PLL Output clock division ratio is controlled by BIT[5:4] of
WM8940_GPIO register(08h).
Current code read/write the WM8940_ADDCNTRL(07h) register which is wrong.

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>