ALSA: scarlett2: Add check for config_item presence

Update scarlett2_usb_get_config() and scarlett2_usb_set_config() to
make sure that the config_item_num is valid for the device.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/b0572b23291ffd1b208f21d298adaf4d9f1fe4bc.1703444932.git.g@b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett2.c

@@ -1528,6 +1528,12 @@ static int scarlett2_usb_get_config(
 	u8 *buf_8;
 	u8 value;
 
+	/* Check that the configuration item is present in the
+	 * configuration set used by this device
+	 */
+	if (!config_item->offset)
+		return -EFAULT;
+
 	/* For byte-sized parameters, retrieve directly into buf */
 	if (config_item->size >= 8) {
 		size = config_item->size / 8 * count;
@@ -1594,6 +1600,12 @@ static int scarlett2_usb_set_config(
 	int offset, size;
 	int err;
 
+	/* Check that the configuration item is present in the
+	 * configuration set used by this device
+	 */
+	if (!config_item->offset)
+		return -EFAULT;
+
 	/* Cancel any pending NVRAM save */
 	cancel_delayed_work_sync(&private->work);