A digital DC bias caused by various truncations in the DDC chain was
previously noticable with small signal levels, especially with high
decimation rates. This patch eliminates the bias by replacing the
truncation with rounding or simply keeping more bits for longer where it
makes sense.
This is essentially a forward port of a similar prior fix to the usrp2
DDC chain: https://github.com/EttusResearch/fpga/pull/4.
Signed-off-by: Ryan Volz <ryan.volz@gmail.com>
Original-commit: a57c162a0d11ab82a83c911a94272ceb6f7ff70a
