usb: gadget: udc: renesas-usb3: clear VBOUT bit in DRD_CON

This driver should clear the bit. Otherwise, the VBUS will output
wrongly if the usb port on a board has VBUS output capability.

Fixes: 746bfe63 ("usb: gadget: renesas_usb3: add support for
		      Renesas USB3.0 peripheral controller")
Cc: <stable@vger.kernel.org> # v4.5+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>