DDF: fix detection of failed devices during assembly.

DDF: fix detection of failed devices during assembly.

When we call "getinfo_super", we report the working/failed status
of the particular device, and also (via the 'map') the working/failed
status of every other device that this metadata is aware of.

It is important that the way we calculate "working or failed" is
consistent.
As it is, getinfo_super_ddf() will report a spare as "working", but
every other device will see it as "failed", which leads to failure to
assemble arrays with spares.

For getinfo_super_ddf (i.e. for the container), a device is assumed
"working" unless flagged as DDF_Failed.
For getinfo_super_ddf_bvd (for a member array), a device is assumed
"failed" unless DDF_Online is set, and DDF_Failed is not set.

Reported-by: "David F." <df7729@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>