dt-bindings: usb: dwc2: fix bindings for amlogic, meson-gxbb-usb

The amlogic,meson-gxbb-usb compatible needs snps,dwc2 aswell like other
Amlogic SoC.

Fixes: f3ca745d ("dt-bindings: usb: Convert DWC2 bindings to json-schema")
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Rob Herring <robh@kernel.org>