LU-2504 procfs: Call put_cpu() if stats alloc fails

LU-2504 procfs: Call put_cpu() if stats alloc fails

Call put_cpu() if lprocfs_stats_alloc_one() fails in
lprocfs_stats_lock().

Signed-off-by: John L. Hammond <jhammond@tacc.utexas.edu>
Change-Id: I12c3eb9ecbbef3086493d63c300ddb853d86dd98
Reviewed-on: http://review.whamcloud.com/4845
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>