busybox

nanddump: make oobbuf allocation dynamic

In accordance with upstream mtd-utils commit 96a5eeaf (mtd-utils: nanddump:
Dynamic buffer, increase pagesize/oobsize).

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>