usb: isp1760: isp1760-udc: Provide missing description for 'udc' param

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

 drivers/usb/isp1760/isp1760-udc.c:150: warning: Function parameter or member 'udc' not described in 'isp1760_udc_select_ep'

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rui Miguel Silva <rui.silva@linaro.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: linux-usb@vger.kernel.org
Reviewed-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210526130037.856068-7-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/isp1760/isp1760-udc.c

@@ -137,6 +137,7 @@ static void __isp1760_udc_select_ep(struct isp1760_udc *udc,
 /**
  * isp1760_udc_select_ep - Select an endpoint for register access
  * @ep: The endpoint
+ * @udc: Reference to the device controller
  *
  * The ISP1761 endpoint registers are banked. This function selects the target
  * endpoint for banked register access. The selection remains valid until the