usb: gadget: at91_udc: fix ep maxpacket initialisation

This patch fixes problem with unnecessary usb_ep_set_maxpacket_limit() usage.
It should not be used in at91udc_probe() function, where maxpacket values are
set for field "maxpacket" of struct at91_ep, which is representation of
endpoint in driver internals. Function usb_ep_set_maxpacket_limit() is called
in udc_reinit() function, where struct usb_ep instances are initialised with
values set previously in struct at91_ep instances. So it's very important to
initialise it properly.

Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>