ARM: dts: ls1021a: Harmonize DWC USB3 DT nodes name

In accordance with the DWC USB3 bindings the corresponding node
name is suppose to comply with the Generic USB HCD DT schema, which
requires the USB nodes to have the name acceptable by the regexp:
"^usb(@.*)?" . Make sure the "snps,dwc3"-compatible nodes are correctly
named.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>