ALSA: compress_offload: Add missing descriptions in structs

Add the missing descriptions for snd_compr_ops, snd_compr_task and
snd_compr_task_status fields, in order to shut up the build warnings.

Fixes: 04177158cf98 ("ALSA: compress_offload: introduce accel operation mode")
Reported-by: Stephen Rothwell <[e-mail]>
Closes: https://lore.kernel.org/[e-mail]
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Takashi Iwai <[e-mail]>

include/sound/compress_driver.h

···
  * Not valid if copy is implemented
  * @get_caps: Retrieve DSP capabilities, mandatory
  * @get_codec_caps: Retrieve capabilities for a specific codec, mandatory
+ * @task_create: Create a set of input/output buffers for accel operations
+ * @task_start: Start (queue) a task for accel operations
+ * @task_stop: Stop (dequeue) a task for accel operations
+ * @task_free: Free a set of input/output buffers for accel operations
  */
 struct snd_compr_ops {
 	int (*open)(struct snd_compr_stream *stream);

include/uapi/sound/compress_offload.h

···
  * @output_fd: data output file descriptor (dma-buf)
  * @input_size: filled data in bytes (from caller, must not exceed fragment size)
  * @flags: see SND_COMPRESS_TFLG_* defines
+ * @reserved: reserved for future extension
  */
 struct snd_compr_task {
 	__u64 seqno;
···
  * @output_size: filled data in bytes (from driver)
  * @output_flags: reserved for future (all zeros - from driver)
  * @state: actual task state (SND_COMPRESS_TASK_STATE_*)
+ * @reserved: reserved for future extension
  */
 struct snd_compr_task_status {
 	__u64 seqno;