usb: gadget: android: Cancel pending ctrlrequest before disabling

Make sure there is no pending ctrlrequest before removing the config.
Otherwise the ctrlrequest complete callback could access structures
after they have been freed. Unbind cancels pending transfers but not
ep0 requests.

Bug: 5513065 5440193

Change-Id: I063c22bf5d104a3d2df71cf622409459fac5f27a
Signed-off-by: Benoit Goby <benoit@android.com>