crypto: rsa - comply with crypto_akcipher_maxsize()

crypto_akcipher_maxsize() asks for the output buffer size without
caring for errors. It allways assume that will be called after
a valid setkey. Comply with it and return what he wants.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/rsa.c

@@ -337,11 +337,11 @@ err:
 	return -ENOMEM;
 }
 
-static int rsa_max_size(struct crypto_akcipher *tfm)
+static unsigned int rsa_max_size(struct crypto_akcipher *tfm)
 {
 	struct rsa_mpi_key *pkey = akcipher_tfm_ctx(tfm);
 
-	return pkey->n ? mpi_get_size(pkey->n) : -EINVAL;
+	return mpi_get_size(pkey->n);
 }
 
 static void rsa_exit_tfm(struct crypto_akcipher *tfm)