When creating an initial bad blocks table, create it empty. This is
necessary because when the bad block table blocks are not
initialized (all ff) while some partitions are, all the blocks which
have an OOB data not beginning with 0xff 0xff will be marked as bad
blocks in the initial bad blocks scan.

As a consequence, any existing blocks are impossible to erase
anymore. Fix this by fixing the BBT creation flag.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>