ALSA: seq: Fix missing error handling in snd_seq_timer_open()

snd_seq_timer_open() didn't catch the whole error path but let through
if the timer id is a slave.  This may lead to Oops by accessing the
uninitialized pointer.

 BUG: unable to handle kernel NULL pointer dereference at 00000000000002ae
 IP: [<ffffffff819b3477>] snd_seq_timer_open+0xe7/0x130
 PGD 785cd067 PUD 76964067 PMD 0
 Oops: 0002 [#4] SMP
 CPU 0
 Pid: 4288, comm: trinity-child7 Tainted: G      D W 3.9.0-rc1+ #100 Bochs Bochs
 RIP: 0010:[<ffffffff819b3477>]  [<ffffffff819b3477>] snd_seq_timer_open+0xe7/0x130
 RSP: 0018:ffff88006ece7d38  EFLAGS: 00010246
 RAX: 0000000000000286 RBX: ffff88007851b400 RCX: 0000000000000000
 RDX: 000000000000ffff RSI: ffff88006ece7d58 RDI: ffff88006ece7d38
 RBP: ffff88006ece7d98 R08: 000000000000000a R09: 000000000000fffe
 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
 R13: ffff8800792c5400 R14: 0000000000e8f000 R15: 0000000000000007
 FS:  00007f7aaa650700(0000) GS:ffff88007f800000(0000) GS...

sound/core/seq/seq_timer.c

@@ -290,10 +290,10 @@ int snd_seq_timer_open(struct snd_seq_queue *q)
 			tid.device = SNDRV_TIMER_GLOBAL_SYSTEM;
 			err = snd_timer_open(&t, str, &tid, q->queue);
 		}
-		if (err < 0) {
-			snd_printk(KERN_ERR "seq fatal error: cannot create timer (%i)\n", err);
-			return err;
-		}
+	}
+	if (err < 0) {
+		snd_printk(KERN_ERR "seq fatal error: cannot create timer (%i)\n", err);
+		return err;
 	}
 	t->callback = snd_seq_timer_interrupt;
 	t->callback_data = q;