usb: gadget: udc: net2280: Code cleanout remove ep_stdrsp function

ep_stdrsp was only called by handle_stat0_irqs_superspeed and with
always the same flags.

Remove the function and replace the call by the code inside the
function, since it is very simple once the dead code is removed.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>