UBI: Fastmap: Care about the protection queue

Fastmap can miss a PEB if it is in the protection queue
and not jet in the used tree.
Treat every protected PEB as used.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>