dt-bindings: usb: dwc3-imx8mp: Use the correct name for child node "snps, dwc3"

File snps,dwc3.yaml describes the schema of Synopsys DesignWare USB3
Controller, it directly or indirectly contains "$ref: usb.yaml". So the
node name of "snps,dwc3" must start with "usb". Otherwise, the following
warning will be displayed:

Documentation/devicetree/bindings/usb/fsl,imx8mp-dwc3.example.dt.yaml: \
dwc3@38100000: $nodename:0: 'dwc3@38100000' does not match '^usb(@.*)?'
        From schema: Documentation/devicetree/bindings/usb/snps,dwc3.yaml

In addition, replace "type: object" with "$ref: snps,dwc3.yaml#". Ensure
that all properties of the child node comply with snps,dwc3.yaml.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20210329072714.2135-2-thunder.leizhen@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>