mtd: struct device - replace bus_id with dev_name(), dev_set_name()

Cc: dwmw2@infradead.org
Cc: linux-mtd@lists.infradead.org
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>