arm64: dts: meson-g12b-ugoos-am6: fix usb vbus-supply

The USB supply used the wrong property, fixing:
meson-g12b-ugoos-am6.dt.yaml: usb@ffe09000: 'vbus-regulator' does not match any of the regexes: '^usb@[0-9a-f]+$', 'pinctrl-[0-9]+'

Fixes: 2cd2310f ("arm64: dts: meson-g12b-ugoos-am6: add initial device-tree")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20200326160857.11929-2-narmstrong@baylibre.com