scsi-disk: do not complete requests early for rerror/werror=ignore

When requested to ignore errors, just do nothing and let the
request complete normally.  This means that the request will
be accounted correctly.

This is what commit 40dce4ee ("scsi-disk: fix rerror/werror=ignore",
2018-10-19) was supposed to do:

Fixes: 40dce4ee ("scsi-disk: fix rerror/werror=ignore", 2018-10-19)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>