[MTD] [NAND] plat_nand: set mtd->name

This patch sets mtd->name to the platform bus ID in the plat_nand
driver, so that you can specify partitions readily with mtdparts=.

Currently it relies on nand_base filling in the name from the device,
which results in names like "NAND 256MiB 3,3V 8-bit", that you can't
use with cmdlineparts.

Signed-off-by: Hamish Moffatt <hamish@cloud.net.au>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>