arm64: dts: meson-g12-common: fix dwc2 clock names

Use the correct dwc2 clock name.

Fixes: 9baf7d6b ("arm64: dts: meson: g12a: Add G12A USB nodes")
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/20200326160857.11929-3-narmstrong@baylibre.com