perf test: fix typo in python test

perf test: fix typo in python test

Library loading in python syntax should be 'import perf', not 'use perf'.

Signed-off-by: WANG Chao <chaowang@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jean Pihet <jean.pihet@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1415780826-13250-1-git-send-email-chaowang@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>