perf python: Properly link with libtraceevent

Namhyung Kim reported that the build fails with:

  GEN python/perf.so
  gcc: error: python_ext_build/tmp//../../libtraceevent.a: No such file or directory
  error: command 'gcc' failed with exit status 1
  cp: cannot stat `python_ext_build/lib/perf.so': No such file or directory
  make: *** [python/perf.so] Error 1

We need to propagate the TE_PATH variable to the setup.py file.

Reported-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lkml.kernel.org/n/tip-8umiPbm4sxpknKivbjgykhut@git.kernel.org
[ Fixed superfluous variable build error. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>