UBI: initialize LEB number variable

UBI: initialize LEB number variable

commit f16db8071ce18819fbd705ddcc91c6f392fb61f8 upstream.

In some of the 'out_not_moved' error paths, lnum may be used
uninitialized. Don't ignore the warning; let's fix it.

This uninitialized variable doesn't have much visible effect in the end,
since we just schedule the PEB for erasure, and its LEB number doesn't
really matter (it just gets printed in debug messages). But let's get it
straight anyway.

Coverity CID #113449

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>