imsm: fix: correct checking volume's degradation

imsm: fix: correct checking volume's degradation

We do not check the return value of sysfs_get_ll() now. It is wrong.
If reading of the sysfs "degraded" key does not succeed,
the "new_degraded" variable will not be initiated
and accidentally it can have the value of "degraded" variable.
In that case the change of degradation will not be checked.

It happens if mdadm is compiled with gcc's "-fstack-protector" option
when one tries to stop a volume under reshape (e.g. OLCE).
Reshape seems to be finished then (metadata is in normal/clean state)
but it is not finished, it is broken and data are corrupted.

Now we always check the return value of sysfs_get_ll().
Even if reading of the sysfs "degraded" key does not succeed
(rv == -1) the change of degradation will be checked.

Signed-off-by: Lukasz Dorau <lukasz.dorau@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>