perf ui/gtk: Fix callchain display

perf ui/gtk: Fix callchain display

With current output field change, GTK browser cannot display callchain
information correctly since it couldn't determine where the symbol
column is.  This is a problem - just for now I changed to use the last
column since it'll work for most cases.

Also it has a same problem of the percentage as stdio code.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Arun Sharma <asharma@fb.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/1401335910-16832-25-git-send-email-namhyung@kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>