usb: dwc3: gadget: remove duplicated code from __dwc3_gadget_ep_set_halt

whenever we want to stall ep0, we always call
dwc3_ep0_stall_and_restart() which makes sure
to send ep0state properly rendering the code
in __dwc3_gadget_ep_set_halt() duplicated.

Reported-by: Pratyush Anand <pratyush.anand@st.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>