The powerdown pin for the second camera is gpio3_b5 not b4,
so fix that. We don't have a working camera setup yet, so this
is not really critical, but nevertheless better to have fixed
already.

Fixes: 36ead914 ("ARM: dts: rockchip: add BQ Edison 2 QC devicetree")
Reported-by: Johan Jonker <jbx6244@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>