ASoC: arizona: Correct return value of arizona_is_enabled_fll

arizona_is_enabled_fll currently returns a bool, but can throw an error.
The error will be basically ignored and we will treat the FLL as already
on. This patch changes the return to be an int and adds error code to
propagate the error up to the callback.

Reported-by: Anil Kumar <anil.kumar@wolfsonmicro.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>