perf tools: Fix pipe check regression in attr event callback

perf tools: Fix pipe check regression in attr event callback

The file factoring in builtin-inject.c object introduced regression
in attr event callback. The commit is:
  02a1d44 perf inject: Handle output file via perf_data_file object

Following hunk reversed the logic:
  -       if (!inject->pipe_output)
  +       if (&inject->output.is_pipe)

putting it back, following example now works:
  $ perf record -o - kill | perf inject -b | perf report -i -

Plus removing extra '&' (kudos to Arnaldo)

Reported-by: Stephane Eranian <eranian@google.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
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/20140605204117.GA1771@krava.redhat.com
Signed-off-by: Jiri Olsa <jolsa@kernel.org>