drive_init() picks the first free bus and unit number, unless the user
specifies them.

This isn't a good fit for the drive_add monitor command, because there
we specify the controller by PCI address instead of using bus number
set by drive_init().

scsi_hot_add() takes care to replace the unit number set by
drive_init() by the real one, but it neglects to replace the bus
number.  Thus, bus/unit in DriveInfo may be bogus.  Affects
drive_get() and drive_get_max_bus().  I'm not aware of anything bad
happening because of that; looks like by the time we're hot-plugging,
the two functions aren't used anymore.  Fix it anyway.

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