serial/uart_rpmsg: should init the lock before call rpmsg_register_callback

To avoid init the lock after this lock has been used.

Signed-off-by: Bowen Wang <wangbowen6@xiaomi.com>
diff --git a/drivers/serial/uart_rpmsg.c b/drivers/serial/uart_rpmsg.c
index 303ebf8..a3e9e7a 100644
--- a/drivers/serial/uart_rpmsg.c
+++ b/drivers/serial/uart_rpmsg.c
@@ -444,6 +444,7 @@
       goto fail;
     }
 
+  nxmutex_init(&priv->lock);
   priv->cpuname = cpuname;
   priv->devname = devname;
 
@@ -456,10 +457,10 @@
                                 NULL);
   if (ret < 0)
     {
+      nxmutex_destroy(&priv->lock);
       goto fail;
     }
 
-  nxmutex_init(&priv->lock);
   snprintf(dev_name, sizeof(dev_name), "%s%s",
            UART_RPMSG_DEV_PREFIX, devname);
   uart_register(dev_name, dev);