nfsd: fix startup order in nfsd_reply_cache_init

If we end up doing "goto out_nomem" in this function, we'll call
nfsd_reply_cache_shutdown. That will attempt to walk the LRU list and
free entries, but that list may not be initialized yet if the server is
starting up for the first time. It's also possible for the shrinker to
kick in before we've initialized the LRU list.

Rearrange the initialization so that the LRU list_head and cache size
are initialized before doing any of the allocations that might fail.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>