extcon: axp288: Use vbus-valid instead of -present to determine cable presence

The vbus-present bit in the power status register also gets set to 1
when a usb-host cable (id-pin shorted to ground) is plugged in and a 5v
boost converter is supplying 5v to the otg usb bus.

This causes a "disconnect or unknown or ID event" warning in dmesg as
well as the extcon device to report the last detected charger cable
type as being connected even though none is connected.

This commit switches to checking the vbus-valid bit instead, which is
only 1 when both vbus is present and the vbus-path is enabled in the
vbus-path control register (the vbus-path gets disabled when a usb-host
cable is detected, to avoid the pmic drawing power from the 5v boost
converter).

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>