NFS: Fix a potential NULL dereference in nfs_get_client()

None of the callers are expecting NULL returns from nfs_get_client() so
this code will lead to an Oops.  It's better to return an error
pointer.  I expect that this is dead code so hopefully no one is
affected.

Fixes: 31434f49 ("nfs: check hostname in nfs_get_client")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/client.c

@@ -406,7 +406,7 @@ struct nfs_client *nfs_get_client(const struct nfs_client_initdata *cl_init)
 
 	if (cl_init->hostname == NULL) {
 		WARN_ON(1);
-		return NULL;
+		return ERR_PTR(-EINVAL);
 	}
 
 	/* see if the client already exists */