usb: dwc2/gadget: avoid disabling ep0

Endpoint 0 should not be disabled, so we start loop counter from number 1.

Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Cc: stable <stable@vger.kernel.org> # 3.16
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>