knfsd: nfsd: remove superfluous assignment from nfsd_lookup

The "err" variable will only be used in the final return, which always happens
after either the preceding

	err = fh_compose(...);

or after the following

	err = nfserrno(host_err);

So the earlier assignment to err is ignored.

Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>