ARM: dts: clps711x: fix missing interrupt parent

The kernelci.org bot reports a build time regression:

arch/arm/boot/dts/ep7209.dtsi:187.17-192.4: Warning (interrupts_property): /keypad: Missing interrupt-parent

There is only one interrupt controller in this SoC, so I assume this
is the parent.

Fixes: 2bd86203 ("ARM: dts: clps711x: Add keypad node")
Reported-by: kernelci.org bot <bot@kernelci.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>