block: vhd: impl DiskFile for FixedVhdDiskAsync

Marker impl bundling DiskSize and Geometry supertraits.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

block/src/fixed_vhd_async.rs

@@ -88,6 +88,8 @@ impl disk_file::Resizable for FixedVhdDiskAsync {
     }
 }
 
+impl disk_file::DiskFile for FixedVhdDiskAsync {}
+
 pub struct FixedVhdAsync {
     raw_file_async: RawFileAsync,
     size: u64,