echoaudio: Fix some long standing bugs

[Mark Hills]

Takashi, thank you for the feedback on the previous patches.

I will follow up with the final patches ready for merging. I've been 
running for many days now against kernel 5.6.14 with all issues resolved 
and no side effects.

I think it would be good to include these in a stable/LTS kernel. Is there 
some criteria, and can you assist with this?

Many thanks

-- 
Mark