ftrace/x86: One more missing sync after fixup of function modification failure

If a failure occurs while modifying ftrace function, it bails out and will
remove the tracepoints to be back to what the code originally was.

There is missing the final sync run across the CPUs after the fix up is done
and before the ftrace int3 handler flag is reset.

Here's the description of the problem:

	CPU0				CPU1
	----				----
  remove_breakpoint();
  modifying_ftrace_code = 0;

				[still sees breakpoint]
				<takes trap>
				[sees modifying_ftrace_code as zero]
				[no breakpoint handler]
				[goto failed case]
				[trap exception - kernel breakpoint, no
				 handler]
				BUG()

Link: http://lkml.kernel.org/r/1393258342-29978-2-git-send-email-pmladek@suse.cz

Fixes: 8a4d0a68

 "ftrace: Use breakpoint method to update ftrace caller"
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>