mtd: nand: omap2: show parent device structure in sysfs

Make sure the device structure is properly shown in sysfs by properly
filling in dev.parent.

While at it, make use of the default owner and name values set by
mtdcore.

Signed-off-by: Frans Klaver <fransklaver@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>