perf symbols: Do not apply symfs for an absolute vmlinux path

If an user gives both of --symfs and --vmlinux option, the vmlinux will
be searched under the symfs directory.  This is somewhat confusing since
vmlinux often lives in kernel build directory or somewhere other than
user space binaries.

So it'd be better not adding symfs prefix for a vmlinux if it has an
absolute pathname.

Reported-by: Kwanghyun Yoo <ykh815.yoo@lge.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: David Ahern <dsahern@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1374048495-3643-1-git-send-email-namhyung@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>