usb: dwc3: fix implementation of endpoint wedge

The dwc3 UDC driver doesn't implement endpoint wedging correctly.
When an endpoint is wedged, the gadget driver should be allowed to
clear the wedge by calling usb_ep_clear_halt().  Only the host is
prevented from resetting the endpoint.

This patch fixes the implementation.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Pratyush Anand <pratyush.anand@st.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>