ARM: dts: ux500: Remove ux500_ prefix from ux500_serial* labels

ux500_serial{0,1,2} are the only labels with ux500_ prefix in
ste-dbx5x0.dtsi, the other labels (gpio0, msp, ...) do not use
any prefix. Remove it for consistency.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20191125170428.76069-4-stephan@gerhold.net


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>