crypto: salsa20-generic - use crypto_xor_cpy()

In salsa20_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/salsa20_generic.c

@@ -86,18 +86,17 @@ static void salsa20_docrypt(u32 *state, u8 *dst, const u8 *src,
 {
 	__le32 stream[SALSA20_BLOCK_SIZE / sizeof(__le32)];
 
-	if (dst != src)
-		memcpy(dst, src, bytes);
-
 	while (bytes >= SALSA20_BLOCK_SIZE) {
 		salsa20_block(state, stream);
-		crypto_xor(dst, (const u8 *)stream, SALSA20_BLOCK_SIZE);
+		crypto_xor_cpy(dst, src, (const u8 *)stream,
+			       SALSA20_BLOCK_SIZE);
 		bytes -= SALSA20_BLOCK_SIZE;
 		dst += SALSA20_BLOCK_SIZE;
+		src += SALSA20_BLOCK_SIZE;
 	}
 	if (bytes) {
 		salsa20_block(state, stream);
-		crypto_xor(dst, (const u8 *)stream, bytes);
+		crypto_xor_cpy(dst, src, (const u8 *)stream, bytes);
 	}
 }