fdkaacdec: Support up to 5 rear channels
The switch (n_rear)
supports up to 5 rear channels, but our channel
set only had space for 3. Size the set properly to fix this.
This didn't actually cause any memory unsafety as PUSH_CHAN
would stop
incrementing n_rear
if the channel set is already full.
Thanks to @alatiera for noticing this.