ARM: 9139/1: kprobes: fix arch_init_kprobes() prototype

ARM: 9139/1: kprobes: fix arch_init_kprobes() prototype

With extra warnings enabled, gcc complains about this function
definition:

arch/arm/probes/kprobes/core.c: In function 'arch_init_kprobes':
arch/arm/probes/kprobes/core.c:465:12: warning: old-style function definition [-Wold-style-definition]
  465 | int __init arch_init_kprobes()

Link: https://lore.kernel.org/all/20201027093057.c685a14b386acacb3c449e3d@kernel.org/
Fixes: 24ba613c9d6c ("ARM kprobes: core code")
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>