MAINTAINERS: Add include/hw/intc/loongson_liointc.h to the Loongson-3 virt section

The corresponding .c file is already listed here, so we should
mention the header here, too.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Song Gao <gaosong@loongson.cn>
Message-ID: <20231017153345.233807-1-thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

MAINTAINERS

@@ -1336,6 +1336,7 @@ F: hw/intc/loongson_liointc.c
 F: hw/mips/loongson3_bootp.c
 F: hw/mips/loongson3_bootp.h
 F: hw/mips/loongson3_virt.c
+F: include/hw/intc/loongson_liointc.h
 F: tests/avocado/machine_mips_loongson3v.py
 
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