Round up the average EC for recovered EB to defer their reuse

[Andrew Worsley]

We suggest rounding up the EC(Erase Count) for recovered EB(Erase Blocks) so
they are less likely than averaged to be re-used. The EBs which have lost their
EC header page and need to be reset are likely to be more worn than average
so it is better to use a larger than average number rather than less than
average number.

        Andrew Worsley