usb: gadget: udc: udc-xilinx: Place correct function names into the headers

usb: gadget: udc: udc-xilinx: Place correct function names into the headers

Fixes the following W=1 kernel build warning(s):

 drivers/usb/gadget/udc/udc-xilinx.c:802: warning: expecting prototype for xudc_ep_enable(). Prototype was for __xudc_ep_enable() instead
 drivers/usb/gadget/udc/udc-xilinx.c:997: warning: expecting prototype for xudc_ep0_queue(). Prototype was for __xudc_ep0_queue() instead

Cc: Felipe Balbi <balbi@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: linux-usb@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210526130037.856068-20-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>