nfsd: remove some dead code in nfsd_create_locked()

We changed this around in f135af1041f ('nfsd: reorganize nfsd_create')
so "dchild" can't be an error pointer any more.  Also, dchild can't be
NULL here (and dput would already handle this even if it was).

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>