qemu-io: Clean up openfile() after commit 2e40134

qemu-io: Clean up openfile() after commit 2e40134

Commit 6db9560 split off the growable case so it can use
bdrv_file_open() instead of bdrv_open() then.  Growable BDSes become
anonymous.  Weird.

Commit 2e40134 folded bdrv_file_open() back into bdrv_open() with new
flag BDRV_O_PROTOCOL.  We still have two bdrv_open() calls, and
growable BDSes remain anonymous.

Circle back to before commit 6db9560: just one call, not anonymous.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>