[update] fix finsh bug

Author: liukangcc

components/finsh/shell.c

@@ -157,17 +157,15 @@ int finsh_getchar(void)
         return -1; /* EOF */
     }
 #else
-    rt_device_t device;
 
     RT_ASSERT(shell != RT_NULL);
 
-    device = shell->device;
-    if (device == RT_NULL)
+    if (shell->device == RT_NULL)
     {
         return -1; /* EOF */
     }
 
-    while (rt_device_read(device, -1, &ch, 1) != 1)
+    while (rt_device_read(shell->device, -1, &ch, 1) != 1)
         rt_sem_take(&shell->rx_sem, RT_WAITING_FOREVER);
 
     return ch;