sparc64: Fix prototype warnings in adi_64.c

Fix the following warnings:
arch/sparc/kernel/adi_64.c:124:21: warning: no previous prototype for ‘find_tag_store’
arch/sparc/kernel/adi_64.c:156:21: warning: no previous prototype for ‘alloc_tag_store’
arch/sparc/kernel/adi_64.c:299:6: warning: no previous prototype for ‘del_tag_store’

None of the functions were used outside the file, so declare them static.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: David S. Miller <davem@davemloft.net>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Tested-by: Andreas Larsson <andreas@gaisler.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20240330-sparc64-warnings-v1-7-37201023ee2f@ravnborg.org
Signed-off-by: Andreas Larsson <andreas@gaisler.com>