UBI reserves an LEB sized buffer for various needs. We can use this buffer
while scanning, instead of allocating another one. This patch was originally
created by Jan Luebbe <jlu@pengutronix.de>, but then he dropped it and I picked
up and tweaked a little bit.
Signed-off-by: NArtem Bityutskiy <artem.bityutskiy@linux.intel.com>