Some error checking was added ca. 2.5.58 that would remove a device from 
its bus's list of devices if device_attach() returned an error. This 
included errors returned from drv->probe(), and the -ENODEV error returned
if the device wasn't bound to any driver.

This was BAD since it was perfectly fine for a device not to bind to a 
driver immediately, and for drivers to return an error on probe() if the 
device doesn't exactly qualify as one it supports. 

This changes device_attach() and driver_attach() to both return void, 
instead of an error, since they really can never fail hard enough to cause
the device or driver to be removed from the bus.