mtd: spi-nor: s/addr_width/addr_nbytes

Address width was an unfortunate name, as it means the number of IO lines
used for the address, whereas in the code it is used as the number of
address bytes. s/addr_width/addr_nbytes throughout the entire SPI NOR
framework.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Michael Walle <michael@walle.cc>
Acked-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20220725092505.446315-2-tudor.ambarus@microchip.com