ALSA: compress: update comment for sample rate in snd_codec

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
(cherry picked from commit d9afee6904caa7cf3c7f417f02e765db89d2b5dc)
Signed-off-by: Yuchen Song <yuchens@nvidia.com>
Change-Id: I7608d924613611222766a898a97c856a64c2eb68