ftrace/fgraph/x86: Have prepare_ftrace_return() take ip as first parameter

The function graph helper function prepare_ftrace_return() which does the work
to hijack the parent pointer has that parent pointer as its first parameter.
Instead, if we make it the second parameter and have ip as the first parameter
(self_addr), then it can use the %rdi from save_mcount_regs that loads it
already.

Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1411262304010.3961@nanos

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>