dt/bindings: arm-boards: Spelling s/pointong/pointing/

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>