Documentation: arm: fix wrong reference number in DT definition

Reference to cpu capacity binding has a wrong number. Fix it.

Reported-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>