ARM: dts: rockchip: fix L3G4200D i2c address on PopMetal-RK3288 board

The i2c address of the three-axis digital gyroscope L3G4200D should be
0x69 according to hardware design.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>