iscsi: pass SCSI status back for SG_IO

Signed-off-by: Vadim Rozenfeld <vrozenfe@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 644c6869)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>