usb: gadget: s3c2410_udc: Fix build error

Pass value instead of address as expected by 'usb_ep_set_maxpacket_limit'.
Fixes the following compilation error introduced by commit e117e742
("usb: gadget: add "maxpacket_limit" field to struct usb_ep"):

drivers/usb/gadget/s3c2410_udc.c: In function ‘s3c2410_udc_reinit’:
drivers/usb/gadget/s3c2410_udc.c:1632:3: error:
cannot take address of bit-field ‘maxpacket’
   usb_ep_set_maxpacket_limit(&ep->ep, &ep->ep.maxpacket);

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Reviewed-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>