ARM: dts: rockchip: Fix the PMU interrupt number for rv1108

According to the Rockchip vendor tree the PMU interrupt number is
76, so fix it accordingly.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Tested-by: Fabio Berton <fabio.berton@ossystems.com.br>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>