mtd: spi-nor: core: Shrink the storage size of the flash_info's addr_nbytes

The maximum number of address bytes in SPI NOR is 4. Shrink the storage
size of the flash_info's addr_nbytes.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Michael Walle <michael@walle.cc>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20220725092505.446315-3-tudor.ambarus@microchip.com