usb: gadget: gr_udc: Return error code when trying to set ep.maxpacket > ep.maxpacket_limit

Make gr_ep_enable fail properly when a call requests a larger ep.maxpacket than
ep.maxpacket_limit.

Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>