extcon: arizona: Use DAPM mutex helper functions

We should be using the helper functions to lock the DAPM mutex not
accessing it directly. There are no ill effects of this as the moment
but it is best practice, and the implementation could be changed in the
future.

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