memmap: Fix SD3 Italian translation that uses ExtHiROM.

Lower Mother 2 hack heuristic score to 3.

memmap.cpp

@@ -1080,7 +1080,7 @@ int CMemory::ScoreHiROM (bool8 skip_header, int32 romoff)
 	// Check for extended HiROM expansion used in Mother 2 Deluxe et al.
 	// Looks for size byte 13 (8MB) and an actual ROM size greater than 4MB
 	if (buf[0xd7] == 13 && CalculatedSize > 1024 * 1024 * 4)
-		score += 5;
+		score += 3;
 
 	if (buf[0xd5] & 0x1)
 		score += 2;