dt-bindings: gpio: mrvl-gpio: Fix the gpio-ranges property

The property specifies a list of GPIO-capable pins. Don't limit it to a
single element as there's  presumably more than one GPIO pin.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lore.kernel.org/r/20210121034130.1381872-2-lkundrak@v3.sk

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>