Driver core: Don't ignore error returns from probing

This patch (as797) fixes device_add() in the driver core.  It needs to
pay attention when the driver for a new device reports an error.

At the same time, since bus_remove_device() undoes the effects of both
bus_add_device() and bus_attach_device(), it needs to check whether
the bus_attach_device step failed.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>