ARM: dts: rockchip: fix MIPI interrupt on rk3288

This isn't currently used by the driver but the correct value is 19
since DSIHOST0 is 51 in the TRM and the GIC offset requires 32 to be
subtracted.

Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>