mtd: mtdconcat: fix NAND OOB write

commit 431e1ecabddcd7cbba237182ddf431771f98bb4c upstream.

Currently mtdconcat is broken for NAND. An attemtpt to create
JFFS2 filesystem on concatenation of several NAND devices fails
with OOB write errors. This patch fixes that problem.

Signed-off-by: Felix Radensky <felix@embedded-sol.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>