crypto: lrw - Free rctx->ext with kzfree

The buffer rctx->ext contains potentially sensitive data and should
be freed with kzfree.

Cc: <stable@vger.kernel.org>
Fixes: 700cb3f5fe75 ("crypto: lrw - Convert to skcipher")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/lrw.c

@@ -317,7 +317,7 @@ static void exit_crypt(struct skcipher_request *req)
 	rctx->left = 0;
 
 	if (rctx->ext)
-		kfree(rctx->ext);
+		kzfree(rctx->ext);
 }
 
 static int do_encrypt(struct skcipher_request *req, int err)