ASoC: SOF: no need to check return value of debugfs_create functions

When calling debugfs functions, there is no need to ever check the
return value.  The function can work or not, but the code logic should
never do something different based on this.

Also, if a debugfs call fails, userspace is notified with an error in
the log, so no need to log the error again.

Because we no longer need to check the return value, there's no need to
save the dentry returned by debugfs.  Just use the dentry in the file
pointer if we really need to figure out the "name" of the file being
opened.

Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Cc: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Cc: alsa-devel@alsa-project.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20190731131716.9764-3-gregkh@linuxfoundation.org
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/sof-priv.h

@@ -230,7 +230,6 @@ enum sof_debugfs_access_type {
 
 /* FS entry for debug files that can expose DSP memories, registers */
 struct snd_sof_dfsentry {
-	struct dentry *dfsentry;
 	size_t size;
 	enum sof_dfsentry_type type;
 	/*