usb: dwc3: otg: Don't set psy type to BATTERY if no charger connected

USB driver incorrectly sets USB power supply type to BATTERY on
charger disconnect. Some userspace client may fail to work properly
by assuming that usb_psy i.e. '/sys/class/power_supply/usb' is
of type battery and subsequent reading of battery status from this
USB supply will fail. Hence, set this to POWER_SUPPLY_TYPE_UNKNOWN.

CRs-fixed: 676051
Change-Id: I0a93b607f8cb328486397fa7bc96ff2177db5a77
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>