UBIFS: always cleanup the recovered LEB

Now when we call 'ubifs_recover_leb()' only for LEBs which are potentially
corrupted (i.e., only for last buds, not for all of them), we can cleanup every
LEB, not only those where we find corruption. The reason - unstable bits. Even
though the LEB may look good now, it might contain unstable bits which may hit
us a bit later.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>