NFSD: nfsd_unlink() clobbers non-zero status returned from fh_fill_pre_attrs()

If fh_fill_pre_attrs() returns a non-zero status, the error flow
takes it through out_unlock, which then overwrites the returned
status code with

	err = nfserrno(host_err);

Fixes: a332018a ("nfsd: handle failure to collect pre/post-op attrs more sanely")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>