Given that add_mtd_device() invokes asprintf() thusly:

  mtd->cdev.name = asprintf("nand%d", mtd->class_dev.id);
  ...
  mtd->param_size.value = asprintf("%u", mtd->size);
  ...
  mtd->cdev_oob.name = asprintf("nand_oob%d", mtd->class_dev.id);

make sure del_mtd_device() frees that in the reverse order.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>