kprobes: Use non RCU traversal APIs on kprobe_tables if possible

Current kprobes uses RCU traversal APIs on kprobe_tables
even if it is safe because kprobe_mutex is locked.

Make those traversals to non-RCU APIs where the kprobe_mutex
is locked.

Link: http://lkml.kernel.org/r/158927056452.27680.9710575332163005121.stgit@devnote2

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>