If using indirect descriptors, you can make the total_sg as large as you
want.  If not, BUG is too serious because the function later returns
-ENOSPC.
Signed-off-by: NRichard W.M. Jones <rjones@redhat.com>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>