lantiq: modify ath9k caldata extraction to reuse caldata.sh

lantiq: modify ath9k caldata extraction to reuse caldata.sh

In lantiq, ath9k caldata extraction is implemented to work in two
alternate "modes", the standard one and another one with swapped
byte pairs.

This rearranges the functions so "standard" use is based on the
caldata.sh library, while only a single local function is required
for the special case.

Note that while the parameter for switching between normal and swab
is removed, the size of the caldata is added to the function calls
to stay consistent.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>