ASoC: wm2000: Fix return of uninitialised varible

Anything that sets ret in wm2000_anc_transition will have immediately
returned anyway as such we will always return an uninitialised ret at the
bottom of the function. Simply replace the return with a return 0;

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>