[MTD] NAND Consolidate references and add back default name setting

We have a type pointer. Make use of it instead of the error prone nand_ids[i]
reference.

The NAND driver used to set default name settings from the chip ID
string for the device. The feature got lost during the rework. Add it back.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>