ide: Remove redundant IDEState member conf

ide: Remove redundant IDEState member conf

Commit 428c149b added IDEState member conf to let commit 0009baf1 find
the BlockConf from there.  It exists only for qdev drives, created via
ide_drive_initfn(), not for drives created via ide_init2().

But for a qdev drive, we can just as well reach its IDEDevice, which
contains the BlockConf.  Do that, and revert the parts of commit
428c149b that add IDEState member conf.

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