Add agc_fast_attack and agc_slow_decay into B/D afsk demod init

[bjpetit]

The agc_fast_attack and agc_slow_decay fields were initialized to 0 in the B/D demodulator. As a result, the level calculations would always come out to 0 resulting in the following...

Jan 04 08:13:25 direwolf[614]: ADEVICE0: Sample rate approx. 44.1 k, 0 errors, receive audio level CH0 0
Jan 04 08:14:33 direwolf[614]: AB4KR-1 audio level = 0(-99/-99) [NONE] ____||
Jan 04 08:14:33 direwolf[614]: Audio input level is too low. Increase so most stations are around 50.

Set the values to the same as A/E demodulator.

Also cleaned up some duplicate assignments in A/E demodulator

[wb2osz]

Thanks for pointing this out.
The issue has been resolved in the dev branch.