SCSI: fcoe: convert bus code to use bus_groups

The bus_attrs field of struct bus_type is going away soon, dev_groups
should be used instead.  This converts the fcoe bus code to use the
correct field.

Cc: Robert Love <robert.w.love@intel.com>
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>