mtd: spi-nor: otp: fix access to security registers in 4 byte mode

The security registers either take a 3 byte or a 4 byte address offset,
depending on the address mode of the flash. Thus just leave the
nor->addr_width as is.

Fixes: cad3193f ("mtd: spi-nor: implement OTP support for Winbond and similar flashes")
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Acked-by: Pratyush Yadav <p.yadav@ti.com>