kprobes/mips: Fix to check double free of insn slot

Fix to check double free of insn_slot at arch_remove_kprobe
as other arches do.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: David Daney <ddaney@caviumnetworks.com>
Cc: Maneesh Soni <manesoni@cisco.com>
Cc: Victor Kamensky <kamensky@cisco.com>
Cc: linux-mips@linux-mips.org
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: yrl.pp-manager.tt@hitachi.com
Cc: systemtap@sourceware.org
Patchwork: https://patchwork.linux-mips.org/patch/5293/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>