dt-bindings: mfd: cirrus,madera: Fix 'interrupts' in example

The 'interrupts' properties takes an irq number, not a phandle, and
'interrupt-parent' isn't needed in examples.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20220119015611.2442819-1-robh@kernel.org