nfsd4: Fix filp leak

23fcf2ec (nfsd4: fix oops on lock failure)

The above patch breaks free path for stp->st_file. If stp was inserted
into sop->so_stateids, we have to free stp->st_file refcount. Because
stp->st_file refcount itself is taken whether or not any refcounts are
taken on the stp->st_file->fi_fds[].

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: stable@kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>