As per binding documentation [1], the DWC3 core should have the "ref",
"bus_early" and "suspend" clocks. As explained in the binding, those
clocks are required for new platforms but not for existing platforms
before commit fe8abf33 ("usb: dwc3: support clocks and resets for
DWC3 core").

However, as those clocks are really treated as required, this ends with
having some annoying messages when the "rockchip,rk3399-dwc3" is used:

[    1.724107] dwc3 fe800000.dwc3: Failed to get clk 'ref': -2
[    1.731893] dwc3 fe900000.dwc3: Failed to get clk 'ref': -2
[    2.495937] dwc3 fe800000.dwc3: Failed to get clk 'ref': -2
[    2.647239] dwc3 fe900000.dwc3: Failed to get clk 'ref': -2

In order to remove those annoying messages, update the DWC3 hardware
module node and add all the required clocks. With this change, both, the
glue node and the DWC3 core node, have the clocks defined, but that's
not really a problem and there isn't a side effect on do this. So, we
can get rid of the annoying get clk error messages.

[1] Documentation/devicetree/bindings/usb/dwc3.txt
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>