usb: dwc3: gadget: Clear DCTL.ULSTCHNGREQ before set

Send a no-action link state change request before the actual request
so DWC3 can send the same request whenever we call
dwc3_gadget_set_link_state().

Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>