[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>
diff --git a/sound/core/control.c b/sound/core/control.c
index 31ad581..ac14426 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -75,6 +75,8 @@
 	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);