Fixes the following warning:
  CC [M]  sound/usb/caiaq/device.o
sound/usb/caiaq/device.c: In function ‘snd_probe’:
sound/usb/caiaq/device.c:500:16: warning: ‘card’ may be used
uninitialized in this function [-Wmaybe-uninitialized]
Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
                     const struct usb_device_id *id)
 {
        int ret;
-       struct snd_card *card;
+       struct snd_card *card = NULL;
        struct usb_device *device = interface_to_usbdev(intf);
 
        ret = create_card(device, intf, &card);