dt-bindings: usb: dwc2: fix compatible of Intel Agilex

Intel Agilex USB DWC2 node is used as compatible with generic snps,dwc2
(just like Altera's Stratix10).

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>