ALSA: x86: Properly manage PCM substream lifetype

The PCM substream is referred not only in the PCM callbacks but also
in the irq handler and in the hotplug/unplug codes.  The latter code
paths don't take the PCM lock, thus the PCM may be released
unexpectedly while calling PCM helper functions or accessing
pcm->runtime fields.

This patch implements a simple refcount to assure the PCM substream
accessibility while the other codes are accessing.  It needed some
code refactoring in the relevant functions for avoiding the doubly
spinlocks.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/x86/intel_hdmi_audio.h

@@ -72,9 +72,10 @@
 #define AUD_CONFIG_CH_MASK	0x70
 
 struct pcm_stream_info {
-	struct snd_pcm_substream	*had_substream;
+	struct snd_pcm_substream *substream;
 	u64		buffer_rendered;
 	u32		ring_buf_size;
+	int substream_refcount;
 };
 
 struct ring_buf_info {