[BUG] MFCC HiFi4 optimized version is broken

[singalsu]

Describe the bug

With (ipc3) testbench run the HiFi3 build and generic C version produce similar output. The HiFi4 build creates totally different output that looks wrong.

To Reproduce

Apply first patch #9207, otherwise load to testbench is not working.
Environment variable SOF_WORKSPACE should be set to top level thesofproject directory

Generic C build

cd $SOF_WORKSPACE/sof
scripts/rebuild-testbench.sh
scripts/build-tools.sh -t

MTL testbench build

export XTENSA_TOOLS_ROOT=~/xtensa/XtDevTools
export ZEPHYR_TOOLCHAIN_VARIANT=xt-clang
scripts/rebuild-testbench.sh -p mtl
source $SOF_WORKSPACE/sof/tools/testbench/build_xt_testbench/xtrun_env.sh

Run MFCC, generic C

cd tools/tune/mfcc
./run_mfcc.sh /usr/share/sounds/alsa/Front_Center.wav

Run MTL build of xt-testbench

$XTENSA_PATH/xt-run ../../testbench/build_xt_testbench/testbench -q -r 16000 -R 16000 -c 1 -n 1 -b S16_LE \
-t ../../build_tools/test/topology/test-playback-ssp5-mclk-0-I2S-mfcc-s16le-s16le-48k-24576k-codec.tplg \
-i in.raw -o mfcc-hifi4.raw 2> /dev/null

Start octave

octave --gui &
[ceps1, t, n] = decode_ceps('mfcc.raw',  13);
[ceps2, t, n] = decode_ceps('mfcc-hifi4.raw',  13);

The leftmost plot is cepstral coefficients for utterance "front center". The rightmost is failed hifi4 code run. HiFi3 code version does not have this issue.

Reproduction Rate
100%

Expected behavior
Similar output as with generic C build and HiFi3.

Impact
Showstopper for MFCC in MTL.

Environment

1. Branch name and commit hash of the 2 repositories: sof (firmware/topology) and linux (kernel driver).
   • Kernel: {SHA}
   • SOF: 0bda13d
2. Name of the topology file
   • Topology: test-playback-ssp5-mclk-0-I2S-mfcc-s16le-s16le-48k-24576k-codec.tplg
3. Name of the platform(s) on which the bug is observed.
   • Platform: MTL on xt-run simulation

Screenshots or console output
If applicable, add a screenshot (drag-and-drop an image), or console logs
(cut-and-paste text and put a code fence (```) before and after, to help
explain the issue.

Please also include the relevant sections from the firmware log and kernel log in the report (and attach the full logs for complete reference). Kernel log is taken from dmesg and firmware log from sof-logger. See https://thesofproject.github.io/latest/developer_guides/debugability/logger/index.html

[kv2019i]

@singalsu @lgirdwood I suggest pushing to to v2.11. We are not using MFCC in any upstream topology yet, so this has no impact to 2.10 release.

[singalsu]

The fix is in #9415.