dmg: use DIV_ROUND_UP

I used the clang-tidy qemu-round check to generate the fix:
https://github.com/elmarco/clang-tools-extra

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>

block/dmg.c

@@ -111,7 +111,7 @@ static void update_max_chunk_size(BDRVDMGState *s, uint32_t chunk,
         uncompressed_sectors = s->sectorcounts[chunk];
         break;
     case 1: /* copy */
-        uncompressed_sectors = (s->lengths[chunk] + 511) / 512;
+        uncompressed_sectors = DIV_ROUND_UP(s->lengths[chunk], 512);
         break;
     case 2: /* zero */
         /* as the all-zeroes block may be large, it is treated specially: the