extcon: arizona: Tidy up transition from mic to headphone detect

Moving from microphone detection to headphone detection is done fairly
haphazardly at the moment, sometimes calling arizona_stop_mic at the
call site sometimes relying on a call inside arizona_identify_headphone.
Simplify all this and always call arizona_stop_mic at the top of
arizona_identify_headphone.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>