crypto: aead - Preserve in-place processing in old_crypt

This patch tries to preserve in-place processing in old_crypt as
various algorithms are optimised for in-place processing where
src == dst.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/aead.c

@@ -107,7 +107,8 @@ static int old_crypt(struct aead_request *req,
 		return crypt(req);
 
 	src = scatterwalk_ffwd(nreq->srcbuf, req->src, req->assoclen);
-	dst = scatterwalk_ffwd(nreq->dstbuf, req->dst, req->assoclen);
+	dst = req->src == req->dst ?
+	      src : scatterwalk_ffwd(nreq->dstbuf, req->dst, req->assoclen);
 
 	aead_request_set_tfm(&nreq->subreq, aead);
 	aead_request_set_callback(&nreq->subreq, aead_request_flags(req),