hw/mips/loongson3_virt: Fix condition of IPI IOCSR connection

hw/mips/loongson3_virt: Fix condition of IPI IOCSR connection

>>>     CID 1547264:  Null pointer dereferences  (REVERSE_INULL)
>>>     Null-checking "ipi" suggests that it may be null, but it has already been dereferenced on all paths leading to the check.

Resolves: Coverity CID 1547264
Link: https://lore.kernel.org/qemu-devel/752417ad-ab72-4fed-8d1f-af41f15bc225@app.fastmail.com/
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240621-loongson3-ipi-follow-v2-2-848eafcbb67e@flygoat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>