vpc: Do not return RAW from block_status

vpc: Do not return RAW from block_status

vpc is not really a passthrough driver, even when using the fixed
subformat (where host and guest offsets are equal).  It should handle
preallocation like all other drivers do, namely by returning
DATA | RECURSE instead of RAW.

There is no tangible difference but the fact that bdrv_is_allocated() no
longer falls through to the protocol layer.

Signed-off-by: Max Reitz <[email protected]>
Message-id: 20190725155512[email protected]
Reviewed-by: John Snow <[email protected]>
Signed-off-by: Max Reitz <[email protected]>