perf script: Add missing calls to Py_DECREF for return values

Signed-off-by: Joseph Schuchart <joseph.schuchart@tu-dresden.de>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Ilsche <thomas.ilsche@tu-dresden.de>
Link: http://lkml.kernel.org/r/53BD4EBF.5050407@tu-dresden.de


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