tracing: Fix ftrace stack trace entries

tracing: Fix ftrace stack trace entries

BugLink: http://bugs.launchpad.net/bugs/981162

commit 01de982abf8c9e10fc3089e10585cd2cc914bdab upstream.

8 hex characters tell only half the tale for 64 bit CPUs,
so use the appropriate length.

Link: http://lkml.kernel.org/r/1332411501-8059-2-git-send-email-wolfgang.mauerer@siemens.com

Signed-off-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Leann Ogasawara <leann.ogasawara@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>