sound: fix check for error condition of register_chrdev()

init_oss_soundcore() compares returned value of register_chrdev()
with -1, while other error codes can be returned.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/sound_core.c

@@ -655,7 +655,7 @@ static void cleanup_oss_soundcore(void)
 static int __init init_oss_soundcore(void)
 {
 	if (preclaim_oss &&
-	    register_chrdev(SOUND_MAJOR, "sound", &soundcore_fops) == -1) {
+	    register_chrdev(SOUND_MAJOR, "sound", &soundcore_fops) < 0) {
 		printk(KERN_ERR "soundcore: sound device already in use.\n");
 		return -EBUSY;
 	}