usb: dwc2: Add missing cleanups when usb_add_gadget_udc() fails

Call dwc2_debugfs_exit() and dwc2_hcd_remove() (if the HCD was enabled
earlier) when usb_add_gadget_udc() has failed. This ensures that the
debugfs entries created by dwc2_debugfs_init() as well as the HCD are
cleaned up in the error path.

Fixes: 207324a3 ("usb: dwc2: Postponed gadget registration to the udc class driver")
Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>