mtd-utils: Support jffs2 flash-erase for large OOB (>32b)

mtd-utils: Support jffs2 flash-erase for large OOB (>32b)

"flash_erase" fails on nand flash with JFFS2 that has OOB size greater than
32 bytes. "flash_erase" uses "MEMGETOOSEL" to determine OOB size. This ioctl
call is obsolete and returns error if OOB size is more than 32 bytes.

This patch fixes this issue by using "mtd_write" to update clean-marker
instead of mtd_oob_write. This fix is based on the discussion:
http://lists.infradead.org/pipermail/linux-mtd/2011-September/037958.html.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>