drivers: hv: additional switch to use mb() instead of smp_mb()

commit e4af376d(drivers: hv: switch to use mb() instead of smp_mb()),
the adjustment mistakenly dropped the change in hv_ringbuffer_read,
so add it.
Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/hv/ring_buffer.c

@@ -485,7 +485,7 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
 	/* Make sure all reads are done before we update the read index since */
 	/* the writer may start writing to the read area once the read index */
 	/*is updated */
-	smp_mb();
+	mb();
 
 	/* Update the read index */
 	hv_set_next_read_location(inring_info, next_read_location);