nfsd: Make two functions static

Fix sparse warnings:

fs/nfsd/nfs4state.c:1908:6: warning: symbol 'drop_client' was not declared. Should it be static?
fs/nfsd/nfs4state.c:2518:6: warning: symbol 'force_expire_client' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -1905,7 +1905,7 @@ static void __free_client(struct kref *k)
 	kmem_cache_free(client_slab, clp);
 }
 
-void drop_client(struct nfs4_client *clp)
+static void drop_client(struct nfs4_client *clp)
 {
 	kref_put(&clp->cl_nfsdfs.cl_ref, __free_client);
 }
@@ -2515,7 +2515,7 @@ static const struct file_operations client_states_fops = {
  * so the caller has a guarantee that the client's locks are gone by
  * the time the write returns:
  */
-void force_expire_client(struct nfs4_client *clp)
+static void force_expire_client(struct nfs4_client *clp)
 {
 	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
 	bool already_expired;