vt82c686.c: don't raise SCI when PCI_INTERRUPT_PIN isn't setup

vt82c686.c: don't raise SCI when PCI_INTERRUPT_PIN isn't setup

Without this patch, the following patch will triger clan runtime
sanitizer warnings as follows. This patch proactively works around it.
I leave a correct fix to v582c686.c maintainerfix as I'm not sure
about fuloong2e device model.

> MALLOC_PERTURB_=${MALLOC_PERTURB_:-$(( ${RANDOM:-0} % 255 + 1))}
> QTEST_QEMU_IMG=./qemu-img
> G_TEST_DBUS_DAEMON=/home/petmay01/linaro/qemu-for-merges/tests/dbus-vmstate-daemon.sh
> QTEST_QEMU_BINARY=./qemu-system-mips64el tests/qtest/qom-test --tap -k
> PASS 1 qtest-mips64el/qom-test /mips64el/qom/loongson3-virt
> PASS 2 qtest-mips64el/qom-test /mips64el/qom/none
> PASS 3 qtest-mips64el/qom-test /mips64el/qom/magnum
> PASS 4 qtest-mips64el/qom-test /mips64el/qom/mipssim
> PASS 5 qtest-mips64el/qom-test /mips64el/qom/malta
> ../../hw/pci/pci.c:252:30: runtime error: shift exponent -1 is negative
> PASS 6 qtest-mips64el/qom-test /mips64el/qom/fuloong2e
> PASS 7 qtest-mips64el/qom-test /mips64el/qom/boston
> PASS 8 qtest-mips64el/qom-test /mips64el/qom/pica61
>
> and similarly for eg
>
> MALLOC_PERTURB_=${MALLOC_PERTURB_:-$(( ${RANDOM:-0} % 255 + 1))}
> QTEST_QEMU_IMG=./qemu-img
> G_TEST_DBUS_DAEMON=/home/petmay01/linaro/qemu-for-merges/tests/dbus-vmstate-daemon.sh
> QTEST_QEMU_BINARY=./qemu-system-mips64el tests/qtest/endianness-test
> --tap -k
> ../../hw/pci/pci.c:252:30: runtime error: shift exponent -1 is negative
> PASS 1 qtest-mips64el/endianness-test /mips64el/endianness/fuloong2e
> ../../hw/pci/pci.c:252:30: runtime error: shift exponent -1 is negative
> PASS 2 qtest-mips64el/endianness-test /mips64el/endianness/split/fuloong2e
> ../../hw/pci/pci.c:252:30: runtime error: shift exponent -1 is negative
> PASS 3 qtest-mips64el/endianness-test /mips64el/endianness/combine/fuloong2e

Cc: BALATON Zoltan <balaton@eik.bme.hu>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: "Philippe Mathieu-Daudé" <f4bug@amsat.org>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-Id: <62a5fc69e453fb848bfd4794bae1852a75af73c5.1616532563.git.isaku.yamahata@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>