[update] fix finsh bug

Author: liukangcc

components/finsh/shell.c

@@ -162,14 +162,19 @@ int finsh_getchar(void)
     RT_ASSERT(shell != RT_NULL);
 
     device = shell->device;
-    if (device == RT_NULL)
-    {
-        return -1; /* EOF */
-    }
 
     while (rt_device_read(device, -1, &ch, 1) != 1)
+    {        
         rt_sem_take(&shell->rx_sem, RT_WAITING_FOREVER);
-
+        if (shell->device != device)
+        {
+            device = shell->device;
+            if (device == RT_NULL)
+            {
+                return -1;
+            }
+        }
+    }
     return ch;
 #endif /* RT_USING_POSIX_STDIO */
 #else