ALSA: sb8: add a check for request_region

In case request_region fails, the fix returns an error code to
avoid NULL pointer dereference.
Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/sb/sb8.c

@@ -111,6 +111,10 @@ static int snd_sb8_probe(struct device *pdev, unsigned int dev)
 
 	/* block the 0x388 port to avoid PnP conflicts */
 	acard->fm_res = request_region(0x388, 4, "SoundBlaster FM");
+	if (!acard->fm_res) {
+		err = -EBUSY;
+		goto _err;
+	}
 
 	if (port[dev] != SNDRV_AUTO_PORT) {
 		if ((err = snd_sbdsp_create(card, port[dev], irq[dev],