ALSA: pcm_lib - return back hw_ptr_interrupt

Clemens Ladisch noted for hw_ptr_removal in "cleanup & merge hw_ptr
update functions" commit:

"It is possible for the status/delay ioctls to be called when the sound
card's pointer register alreay shows a position at the beginning of the
new period, but immediately before the interrupt is actually executed.
(This happens regularly on a SMP machine with mplayer.)  When that
happens, the code thinks that the position must be at least one period
ahead of the current position and drops an entire buffer of data."

Return back the hw_ptr_interrupt variable. The last interrupt pointer
is always computed from the latest hw_ptr instead of tracking it
separately (in this case all hw_ptr checks and modifications might
influence also hw_ptr_interrupt and it is difficult to keep it
consistent).

Signed-off-by: Jaroslav Kysela <perex@perex.cz>
diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 255ad91..82d4e33 100644
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -635,8 +635,7 @@
 static inline
 snd_pcm_uframes_t get_hw_ptr_period(struct snd_pcm_runtime *runtime)
 {
-	snd_pcm_uframes_t ptr = runtime->status->hw_ptr;
-	return ptr - (ptr % runtime->period_size);
+	return runtime->hw_ptr_interrupt;
 }
 
 /* define extended formats in the recent OSS versions (if any) */