usb: dwc3: gadget: Iterate only over valid endpoints

Make dwc3_gadget_resize_tx_fifos() iterate only over IN
endpoints that are actually present, based on the
num_in_eps parameter. This terminates the loop so as to
prevent dereferencing a potential NULL dwc->eps[i] where
i >= (num_in_eps + num_out_eps).

Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>