ASoC: Fix WM835x Out4 capture enumeration

commit 87831cb6 upstream.

It's the 8th enum of a zero indexed array. This is why I don't let
new drivers use these arrays of enums...

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>