adds the correct offset for the calibration data.
The values are according to the OpenWrt Forum Thread:
"Fritzbox 7430 and wifi".
Link: <https://forum.openwrt.org/t/fritzbox-7430-and-wifi/86944>
Reported-by: RENErica
Signed-off-by: Joel Linn <jl@conductive.de>
[changed commit message]
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>