ASoC: Fix return value of wm8580_set_sysclk()

We can't just pass back the return value of snd_soc_update_bits() as it
will be 1 if a bit changed rather than zero.

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