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: 04177158 ("ALSA: compress_offload: introduce accel operation mode")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/20241028193731.4b0c3788@canb.auug.org.au
Link: https://patch.msgid.link/20241113072304.4447-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>