ALSA: caiaq: Fix unused variable warning

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: e95b9f7f2ee0 ("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.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>