Remove mfence

Author: Cuda-Chen

virtio-snd.c

@@ -301,9 +301,9 @@ typedef struct {
     // PCM frame ring buffer
     virtio_snd_ring_buffer_t ring;
 } virtio_snd_prop_t;
-#define VSND_COMPILER_BARRIER       \
-    do {                            \
-        asm("mfence" ::: "memory"); \
+#define VSND_COMPILER_BARRIER \
+    do {                      \
+        asm("" ::: "memory"); \
     } while (0)
 
 static virtio_snd_config_t vsnd_configs[VSND_DEV_CNT_MAX];