mtd: mtdchar: add missing initializer on raw write

On writes in MODE_RAW the mtd_oob_ops struct is not sufficiently
initialized which may cause nandwrite to fail. With this patch
it is possible to write raw nand/oob data without additional ECC
(either for testing or when some sectors need different oob layout
e.g. bootloader) like
nandwrite  -n -r -o  /dev/mtd0 <myfile>

Signed-off-by: Peter Wippich <pewi@gw-instruments.de>
Cc: stable@kernel.org
Tested-by: Ricard Wanderlof <ricardw@axis.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>