fftfilterbank: insert AC variables in every process callback
fftfilterbank: insert AC variables in every process callback

Summary:
fftfilterbank did not re-insert its AC variables in every process callback.
Fixed.

Test Plan:
Check if the Jenkins Code-Review build succeeds.
Affirm that AC variables should be re-inserted on every process callback.

Reviewers: giso, pmaanen

Reviewed By: giso

Differential Revision: https://dev.openmha.org/D144

HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA