usb: dwc3: gadget: fix ep->maxburst for ep0

commit 6048e4c69d80600baba35856651056860d5d8f5a upstream.

dwc3_gadget_set_ep_config expects maxburst as incremented by 1. So, by
default initialize ep->maxburst to 1 for ep0.

Signed-off-by: Pratyush Anand <pratyush.anand@st.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>