MIPS: dts: loongson: Fix liointc IRQ polarity

All internal liointc interrupts are high level triggered.

Fixes: b1a79260

 ("MIPS: Loongson64: DeviceTree for Loongson-2K1000")
Cc: stable@vger.kernel.org
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>