ALSA: firewire-lib: optimize packet flushing

Trying to flush completed packets is pointless when the pointer
callback was called from the packet completion callback; avoid it.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/firewire/amdtp.h b/sound/firewire/amdtp.h
index 3f13ff6..b680c5e 100644
--- a/sound/firewire/amdtp.h
+++ b/sound/firewire/amdtp.h
@@ -68,6 +68,7 @@
 
 	unsigned int pcm_buffer_pointer;
 	unsigned int pcm_period_pointer;
+	bool pointer_flush;
 };
 
 int amdtp_out_stream_init(struct amdtp_out_stream *s, struct fw_unit *unit,