[device] Avoid repeated calls device_open interface.

Author: Guozhanxin

src/device.c

@@ -233,25 +233,29 @@ rt_err_t rt_device_open(rt_device_t dev, rt_uint16_t oflag)
         return -RT_EBUSY;
     }
 
-    /* call device_open interface */
-    if (device_open != RT_NULL)
+    /* device is not opened or opened by other oflag, call device_open interface */
+    if (!(dev->open_flag & RT_DEVICE_OFLAG_OPEN) ||
+         ((dev->open_flag & RT_DEVICE_OFLAG_MASK) | (oflag & RT_DEVICE_OFLAG_MASK)))
     {
-        result = device_open(dev, oflag);
-    }
-    else
-    {
-        /* set open flag */
-        dev->open_flag = (oflag & RT_DEVICE_OFLAG_MASK);
+        if (device_open != RT_NULL)
+        {
+            result = device_open(dev, oflag);
+        }
+        else
+        {
+            /* set open flag */
+            dev->open_flag = (oflag & RT_DEVICE_OFLAG_MASK);
+        }
     }
-
+        
     /* set open flag */
     if (result == RT_EOK || result == -RT_ENOSYS)
     {
         dev->open_flag |= RT_DEVICE_OFLAG_OPEN;
 
         dev->ref_count++;
         /* don't let bad things happen silently. If you are bitten by this assert,
-         * please set the ref_count to a bigger type. */
+        * please set the ref_count to a bigger type. */
         RT_ASSERT(dev->ref_count != 0);
     }