mtd: spi-nor: stop (ab)using struct spi_device_id

Using struct spi_device_id for storing list of flash devices comes from
early SPI NOR framework days. Thanks to the commit 70f3ce05 ("mtd:
spi-nor: make spi_nor_scan() take a chip type name, not spi_device_id")
we can stop using spi_device_id and just switch to our own struct.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>