speech-recognition: Fix issues with software inference engine

It seems like the speech recognition DSP task which is collecting
the input data from ROM/VSI audio source needs to be a bit
slower as in case of using software to do the ML inference the
performance is way slower than using the Ethos-NPU which means the
DSP task must be delayed for sometime as to allow some extra time
for the software inference to be finished.

Signed-off-by: Ahmed Ismail <Ahmed.Ismail@arm.com>