scsi: ibmvscsi_tgt: remove use of class_attrs

The class_attrs pointer is going away and it's not even being used in
this driver, so just remove it entirely.

Acked-by: "Bryant G. Ly" <bryantly@linux.vnet.ibm.com>
Cc: Michael Cyr <mikecyr@linux.vnet.ibm.com>
Cc: "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: <linux-scsi@vger.kernel.org>
Cc: <target-devel@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>