perf tools: Fix lsdir to set errno correctly

perf tools: Fix lsdir to set errno correctly

Fix lsdir() to set correct positive error number (ENOMEM).  Since
"errno" must have a positive error number instead of negative number,
fix lsdir to set it correctly.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Hemant Kumar <hemant@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: 8be0a19d36db ("perf tools: Add lsdir() helper to read a directory")
Link: http://lkml.kernel.org/r/20160511135127.23943.40644.stgit@devbox
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>