UBI: initialise update marker

The in kernel copy of a volume's update marker is not initialised from the
volume table. This means that volumes where an update was unfinnished will
not be treated as "forbidden to use". This is basically that the update
functionality was broken.

Signed-off-by: Peter Horton <zero@colonel-panic.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: stable@kernel.org