pcm: fix the snd_pcm_plugin_status() avail and delay fields

pcm: fix the snd_pcm_plugin_status() avail and delay fields

The avail and delay fields in the returned status structure does not
reflect the actual hw_ptr/appl_ptr. This change correct this.

TODO: Unfortunately, the delay might contain also information about
extra hardware / buffering delay which is hidden with this change.

Link: https://lore.kernel.org/alsa-devel/d9c1f37e-5c8d-f289-270e-c6cda7a56ce3@axis.com/
Reported-by: Jonas Holmberg <jonashg@axis.com>
Tested-by: Jonas Holmberg <jonashg@axis.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>