um: virtio_uml: mark device as unregistered when breaking it

[ Upstream commit 8e9cd851 ]

Mark the device as not registered anymore when scheduling the work to
remove it. Otherwise we could end up scheduling the work multiple times
in a row, including scheduling it while it is already running.

Fixes: af9fb41e ("um: virtio_uml: Fix broken device handling in time-travel")
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sashal@kernel.org>