knfsd: Remove dead code from nfsd_cache_lookup

The preallocated cache entry is always set to type RC_NOCACHE, and that
type isn't changed until we later call nfsd_cache_update().

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>