qcow2: cleanup qcow2_co_pwritev_compressed to avoid the recursion

qcow2: cleanup qcow2_co_pwritev_compressed to avoid the recursion

Now that the function uses a vector instead of a buffer, there is no
need to use recursive code.

Signed-off-by: Pavel Butsykin <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Denis V. Lunev <[email protected]>
CC: Jeff Cody <[email protected]>
CC: Markus Armbruster <[email protected]>
CC: Eric Blake <[email protected]>
CC: John Snow <[email protected]>
CC: Stefan Hajnoczi <[email protected]>
CC: Kevin Wolf <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>