Exit enteringAccessoryMode when entered.

... so that a quick usb plug -> unplug actually causes both enter and
exit. Before the second update was treated as another enter.

Admittedly treating any first update as connect and any second update as
disconnect is sketchy, but this was the intention of the current code,
so just fix that for now.

Fixes: 29377436
Change-Id: Ib6bcc23ce5ec9979edcc38952a9414683513ca0c