Fix latent deadlock in DSOUND_callback.

diff --git a/dlls/dsound/mixer.c b/dlls/dsound/mixer.c
index e04ccb3..e187fb8 100644
--- a/dlls/dsound/mixer.c
+++ b/dlls/dsound/mixer.c
@@ -1030,7 +1030,7 @@
 		/* queue new buffer if we have data for it */
 		if (inq>1) DSOUND_WaveQueue(This, inq-1);
 #ifdef SYNC_CALLBACK
-		LeaveCriticalSection(&(This->lock));
+		LeaveCriticalSection(&(This->mixlock));
 #endif
 	}
 	TRACE("completed\n");