NFSv4.2: Fix a reference leak in nfs42_proc_layoutstats_generic

commit 3f807e5ae5597bd65a6fff684083e8eaa21f3fa7 upstream.

The caller of rpc_run_task also gets a reference that must be put.

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>