usb: dwc2: Add msleep for host-only

Although a host-only controller should not have any associated delay,
some rockchip SOC platforms will not show the correct host-values of
registers until after a delay.

So add a 50 ms sleep when in host-only mode.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>