dt-bindings: apple,aic: Fix required item "apple,fiq-index" in affinity description

The required list used "fiq-index" instead of "apple,fiq-index"
described as property and used in the dts. Add the missing "apple,"
prefix.

Fixes: dba07ad1 ("dt-bindings: apple,aic: Add affinity description for per-cpu pseudo-interrupts")
Signed-off-by: Janne Grunau <j@jannau.net>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220909135103.98179-2-j@jannau.net


Signed-off-by: Rob Herring <robh@kernel.org>