scsi-disk: pass sense correctly for guest-recoverable errors

When an error was passed down to the guest because it was recoverable,
the sense length was not copied from the SG_IO data.  As a result,
the guest saw the CHECK CONDITION status but not the sense data.

Signed-off-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>