BMessage: Fix R5 checksum calculation on 64-bit.

Change-Id: I0d418883bb66c6ad9e351c955e213f5cbc975e56
Reviewed-on: https://review.haiku-os.org/c/1336
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

src/kits/app/MessageUtils.cpp

@@ -22,11 +22,7 @@ CalculateChecksum(const uint8 *buffer, int32 size)
 	uint32 temp = 0;
 
 	while (size > 3) {
-#if defined(__i386__)
-		sum += B_SWAP_INT32(*(int32 *)buffer);
-#else
-		sum += *(int32 *)buffer;
-#endif
+		sum += B_BENDIAN_TO_HOST_INT32(*(int32 *)buffer);
 		buffer += 4;
 		size -= 4;
 	}