ARM: dts: pxa3xx: Fix up encoding of the /gpio interrupts property

This way the device tree validator learns that each cell of the property
constitutes a separate item. Otherwise it gets unnecessairly upset:

  pxa300-raumfeld-speaker-s.dt.yaml: gpio@40e00000: interrupts:
      [[8, 9, 10]] is too short

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Robert Jarzmik <robert.jarzmik@free.fr.>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>