crypto: chacha-generic - use crypto_xor_cpy()

In chacha_docrypt(), use crypto_xor_cpy() instead of crypto_xor().
This avoids having to memcpy() the src buffer to the dst buffer.
Signed-off-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

crypto/chacha_generic.c

@@ -22,18 +22,16 @@ static void chacha_docrypt(u32 *state, u8 *dst, const u8 *src,
 	/* aligned to potentially speed up crypto_xor() */
 	u8 stream[CHACHA_BLOCK_SIZE] __aligned(sizeof(long));
 
-	if (dst != src)
-		memcpy(dst, src, bytes);
-
 	while (bytes >= CHACHA_BLOCK_SIZE) {
 		chacha_block(state, stream, nrounds);
-		crypto_xor(dst, stream, CHACHA_BLOCK_SIZE);
+		crypto_xor_cpy(dst, src, stream, CHACHA_BLOCK_SIZE);
 		bytes -= CHACHA_BLOCK_SIZE;
 		dst += CHACHA_BLOCK_SIZE;
+		src += CHACHA_BLOCK_SIZE;
 	}
 	if (bytes) {
 		chacha_block(state, stream, nrounds);
-		crypto_xor(dst, stream, bytes);
+		crypto_xor_cpy(dst, src, stream, bytes);
 	}
 }