mtd: spi-nor: Fix selection of 4-byte addressing opcodes on Spansion

mtd->size is still unassigned when running spansion_post_sfdp_fixups()
hook, therefore use nor->params.size to determine the size of flash device.

This makes sure that 4-byte addressing opcodes are used on Spansion
flashes that are larger than 16MiB and don't have SFDP 4BAIT table
populated.

Fixes: 92094ebc

 ("mtd: spi-nor: Add spansion_post_sfdp_fixups()")
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>