Use EVP_MAX_MD_SIZE to size the Finished message.

That comment is wrong as of TLS 1.2.

Change-Id: I900d5efc09d7468f2601d85f867833e43d046f6a
Reviewed-on: https://boringssl-review.googlesource.com/2603
Reviewed-by: Adam Langley <agl@google.com>

ssl/s3_both.c

@@ -238,7 +238,7 @@ int ssl3_get_finished(SSL *s, int a, int b)
 		a,
 		b,
 		SSL3_MT_FINISHED,
-		64, /* should actually be 36+4 :-) */
+		EVP_MAX_MD_SIZE,
 		SSL_GET_MESSAGE_DONT_HASH_MESSAGE,
 		&ok);