usb: dwc3: gadget: Fix dwc3_stop_active_transfer for synchronization delay

dwc3_stop_active_transfer has been called from two places. After each
calling of this function , we should allow 100 us delay to synchronize
with interconnect.

It would be better if we put this delay in that function only, rather
than into calling routine of this function.

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