[ALSA] Fix substream selection in PCM and rawmidi

The PCM and rawmidi substreams can be selected explicitly by opening
control handle and set via *_PREFER_SUBDEVICE ioctl.  But, when
multiple controls are opened, the driver gets confused.
The patch fixes the initialization of prefer_*_subdevice and the
check of multiple controls.  The first set subdevice is picked up
as the valid one.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/core/control.c

@@ -75,6 +75,8 @@ static int snd_ctl_open(struct inode *inode, struct file *file)
 	init_waitqueue_head(&ctl->change_sleep);
 	spin_lock_init(&ctl->read_lock);
 	ctl->card = card;
+	ctl->prefer_pcm_subdevice = -1;
+	ctl->prefer_rawmidi_subdevice = -1;
 	ctl->pid = current->pid;
 	file->private_data = ctl;
 	write_lock_irqsave(&card->ctl_files_rwlock, flags);

sound/core/pcm.c

@@ -792,6 +792,7 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream,
 		kctl = snd_ctl_file(list);
 		if (kctl->pid == current->pid) {
 			prefer_subdevice = kctl->prefer_pcm_subdevice;
+			if (prefer_subdevice != -1)
 				break;
 		}
 	}

sound/core/rawmidi.c

@@ -430,6 +430,7 @@ static int snd_rawmidi_open(struct inode *inode, struct file *file)
 			kctl = snd_ctl_file(list);
 			if (kctl->pid == current->pid) {
 				subdevice = kctl->prefer_rawmidi_subdevice;
+				if (subdevice != -1)
 					break;
 			}
 		}