mtd: mtdswap: remove useless if (!mtd->ecclayout) test

If the MTD device does not have OOB, the mtd->oobsize and mtd->oobavail
fields are set to zero, and we are testing those values in the following
test.
Remove the useless if (!mtd->ecclayout) test.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>