eal: fix multi-process hotplug rollback

eal: fix multi-process hotplug rollback

If a device fails to attach before it's plugged,
the subsequent rollback will still try to detach it,
causing a segfault. Unplugging a device that wasn't
plugged isn't really supported, so this patch adds
an extra error check to prevent that from happening.

While here, fix this also for normal (non-rollback)
detach, which could also theoretically segfault on
non-plugged device.

Fixes: 244d5130719c ("eal: enable hotplug on multi-process")

Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>