staging: vchiq_arm: mark vchiq_platform_init() static

staging: vchiq_arm: mark vchiq_platform_init() static

This function has no callers from other files, and the declaration
was removed a while ago, causing a W=1 warning:

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c:465:5: error: no previous prototype for 'vchiq_platform_init'

Marking it static solves this problem but introduces a new warning
since gcc determines that 'g_fragments_base' is never initialized
in some kernel configurations:

In file included from include/linux/string.h:254,
                 from include/linux/bitmap.h:11,
                 from include/linux/cpumask.h:12,
                 from include/linux/mm_types_task.h:14,
                 from include/linux/mm_types.h:5,
                 from include/linux/buildid.h:5,
                 from include/linux/module.h:14,
                 from drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c:8:
In function 'memcpy_to_page',
    inlined from 'free_pagelist' at drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c:433:4:
include/linux/fortify-string.h:57:33: error: argument 2 null where non-null expected [-Werror=nonnull]
include/linux/highmem.h:427:9: note: in expansion of macro 'memcpy'
  427 |         memcpy(to + offset, from, len);
      |         ^~~~~~

Add a NULL pointer check for this in addition to the static annotation
to avoid both.

Fixes: 89cc4218f640 ("staging: vchiq_arm: drop unnecessary declarations")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Link: https://lore.kernel.org/r/20230516202603.560554-1-arnd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>