MIPS: DTS: Fix number of msi vectors for Loongson64G

HT irqs vectors are 8 groups, each group has 32 irqs, Loongson64C CPUs
can use only 4 groups and Loongson64G CPUs can use all 8 groups. So the
number of msi vectors of Loongson64G is 192 (32*8 - 64 = 192).

Fixes: 24af1059 ("MIPS: Loongson64: DeviceTree for LS7A PCH")
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>