hw/net/rtl8139: Update coding style to make checkpatch.pl happy

We will modify this code in the next commit. Clean it up
first to avoid checkpatch.pl errors.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>
diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c
index ef32115..be9a0af 100644
--- a/hw/net/rtl8139.c
+++ b/hw/net/rtl8139.c
@@ -799,10 +799,12 @@
     int avail;
 
     /* Receive (drop) packets if card is disabled.  */
-    if (!s->clock_enabled)
-      return 1;
-    if (!rtl8139_receiver_enabled(s))
-      return 1;
+    if (!s->clock_enabled) {
+        return 1;
+    }
+    if (!rtl8139_receiver_enabled(s)) {
+        return 1;
+    }
 
     if (rtl8139_cp_receiver_enabled(s) && rtl8139_cp_rx_valid(s)) {
         /* ??? Flow control not implemented in c+ mode.