powerpc: io-defs.h:43:1: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic]

[Naresh Kamboju]

The Powerpc clang builds failed due to following warnings / errors on the
Linux next-20240416 tag.

Powerpc:
 - tqm8xx_defconfig + clang-17 - Failed
 - allnoconfig + clang-17 - Failed
 - tinyconfig + clang-17 - Failed

Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>

Build log:
--------
In file included from arch/powerpc/kernel/ptrace/ptrace.c:19:
In file included from include/linux/syscalls.h:93:
In file included from include/trace/syscall.h:7:
In file included from include/linux/trace_events.h:9:
In file included from include/linux/hardirq.h:11:
In file included from arch/powerpc/include/asm/hardirq.h:6:
In file included from include/linux/irq.h:20:
In file included from include/linux/io.h:14:
In file included from arch/powerpc/include/asm/io.h:672:
arch/powerpc/include/asm/io-defs.h:43:1: error: performing pointer
arithmetic on a null pointer has undefined behavior
[-Werror,-Wnull-pointer-arithmetic]
   43 | DEF_PCI_AC_NORET(insb, (unsigned long p, void *b, unsigned long c),
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   44 |                  (p, b, c), pio, p)
      |                  ~~~~~~~~~~~~~~~~~~

Links:
 - https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20240416/testrun/23495171/suite/build/test/clang-17-tqm8xx_defconfig/details/
 - https://storage.tuxsuite.com/public/linaro/lkft/builds/2fAvI3mKJ0dTHcazPrLl2zNF9JO/

--
Linaro LKFT
https://lkft.linaro.org