mtd: remove unneeded initializer in mtd_ooblayout_{get, set}_bytes()

There is no need to initialize oobregion and section since they will
be filled by mtd_ooblayout_find_region().

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>