usb: dwc3: gadget: Release gadget lock when handling suspend/resume

gadget_driver suspend/resume operations might require some
dwc3-gadget operations, such as enabling and disabling
endpoints. If the lock is not released, this can cause a
deadlock scenario.

Change-Id: I1e12de65e40492b115ab35de78c2352730649db5
Signed-off-by: Bar Weiner <bweiner@codeaurora.org>