perf tools: Fix error path to do closedir() when synthesizing threads

perf tools: Fix error path to do closedir() when synthesizing threads

When traversing /proc to synthesize the PERF_RECORD_FORK et al events we
were bailing out on errors without calling closedir(), fix it.

Reported-by: David Ahern <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Don Zickus <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>