extcon: arizona: Ensure variables are set for headphone detection

The detecting flag really refers to the microphone detection stage and
as such should be cleared before arizona_identify_headphones is called.
Also the mic flag should be set before identify headphones is called as
well.

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