dt-bindings: usb: qcom,dwc3: correct SDM660 clocks

SDM660 SoC has two instances of DWC3 USB controller: one supporting USB
3.0 and one supporting only up to USB 2.0.  The latter one does not use
iface clock, so allow such variant to fix dtbs_check warnings:

  sda660-inforce-ifc6560.dtb: usb@c2f8800: clocks: [[37, 48], [37, 88], [37, 89], [37, 90]] is too short
  sda660-inforce-ifc6560.dtb: usb@c2f8800: clock-names:2: 'iface' was expected

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230723141550.90223-2-krzysztof.kozlowski@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>