ALSA: caiaq: Fix unused variable warning

The recent cleanup of caiaq driver forgot to remove the unused loop
variable:
sound/usb/caiaq/audio.c: In function 'snd_usb_caiaq_pcm_prepare':
sound/usb/caiaq/audio.c:179:41: error: unused variable 'i' [-Werror=unused-variable]

Fixes: e95b9f7f ("ALSA: snd-usb-caiaq: use snd_pcm_rate_to_rate_bit")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/20240809112252.5af8025f@canb.auug.org.au
Link: https://patch.msgid.link/20240809074254.5290-1-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/caiaq/audio.c

@@ -176,7 +176,7 @@ static int snd_usb_caiaq_pcm_hw_free(struct snd_pcm_substream *sub)
 
 static int snd_usb_caiaq_pcm_prepare(struct snd_pcm_substream *substream)
 {
-	int bytes_per_sample, bpp, ret, i;
+	int bytes_per_sample, bpp, ret;
 	int index = substream->number;
 	struct snd_usb_caiaqdev *cdev = snd_pcm_substream_chip(substream);
 	struct snd_pcm_runtime *runtime = substream->runtime;