ASoC: wm8940: Fix a typo for the mask of setting WM8940_BCLKDIV

The registers are 16 bits, thus remove an extra F for the mask.

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>