regulator: dt-bindings: qcom,usb-vbus-regulator: change node name

usb-vbus-regulator is a better generic node name than dcdc to change the
example to match.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Link: https://lore.kernel.org/r/20221229191542.123367-1-luca@z3ntu.xyz


Signed-off-by: Mark Brown <broonie@kernel.org>