plugins/fmcomms2_adv: Fix DDS broken by libini2 merge

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
plugins/fmcomms6: Convert to use new libini2 code

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
plugins/fmcomms5: Convert to use new libini2 code

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>