nfsd: don't run get_file if nfs4_preprocess_stateid_op return error

commit b022032e195ffca83d7002d6b84297d796ed443b upstream.

we should return error status directly when nfs4_preprocess_stateid_op
return error.

Signed-off-by: fanchaoting <fanchaoting@cn.fujitsu.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>