ASoC: wm_adsp: Put debugfs_remove_recursive back in

This patch reverts commit acbf58e5 ("ASoC: wm_adsp: Let
soc_cleanup_component_debugfs remove debugfs"), and adds an
alternate solution to the issue. That patch removes the call to
debugfs_remove_recursive, which cleans up the DSPs debugfs. The
intention was to avoid an unbinding issue on an out of tree
driver/platform.

The issue with the patch is it means the driver no longer cleans up
its own debugfs, instead relying on ASoC to remove recurive on the
parent debugfs node. This is conceptually rather unclean, but also it
would prevent DSPs being added/removed independently of ASoC and soon
we are going to be upstreaming some non-audio parts with these DSPs,
which will require this.

Finally, it seems the issue on the platform is a result of the
wm_adsp2_cleanup_debugfs getting called twice. This is very likely a
problem on the platform side and will be resolved there. But in the mean
time make the code a little more robust to such issues, and again
conceptually a bit nicer, but clearing the debugfs_root variable in the
DSP structure when the debugfs is removed.

Fixes: acbf58e5 ("ASoC: wm_adsp: Let soc_cleanup_component_debugfs remove debugfs"
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20210824101552.1119-1-ckeepax@opensource.cirrus.com


Signed-off-by: Mark Brown <broonie@kernel.org>