drivers/net/phy: fix kernel-doc notation

Fix kernel-doc warning:
Warning(linux-2.6.25-git11//drivers/net/phy/phy_device.c:275): No
description found for parameter 'bus_id'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>