MAINTAINERS: Update Loongson64 entry

To include newly added irqchip drivers.
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

MAINTAINERS

@@ -11169,6 +11169,7 @@ S:	Maintained
 F:	arch/mips/loongson64/
 F:	arch/mips/include/asm/mach-loongson64/
 F:	drivers/platform/mips/cpu_hwmon.c
+F:	drivers/irqchip/irq-loongson*
 F:	drivers/*/*loongson3*
 F:	drivers/*/*/*loongson3*