Update aes.h

fixed missing multiple returns on mbedtls_aes_setkey_enc
diff --git a/include/mbedtls/aes.h b/include/mbedtls/aes.h
index c82d39a..3c5b133 100644
--- a/include/mbedtls/aes.h
+++ b/include/mbedtls/aes.h
@@ -116,7 +116,7 @@
  *                 <li>256 bits</li></ul>
  *
  * \return         \c 0 on success.
- *                 #MBEDTLS_ERR_AES_INVALID_KEY_LENGTH on failure.
+ * \return         #MBEDTLS_ERR_AES_INVALID_KEY_LENGTH on failure.
  */
 int mbedtls_aes_setkey_enc( mbedtls_aes_context *ctx, const unsigned char *key,
                     unsigned int keybits );