fs.h: fix a comment in file_operations

include/nuttx/fs/fs.h

@@ -225,10 +225,11 @@ struct file_operations
                        FAR struct mm_map_entry_s *map);
   CODE int     (*truncate)(FAR struct file *filep, off_t length);
 
-  /* The two structures need not be common after this point */
-
   CODE int     (*poll)(FAR struct file *filep, FAR struct pollfd *fds,
                        bool setup);
+
+  /* The two structures need not be common after this point */
+
 #ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
   CODE int     (*unlink)(FAR struct inode *inode);
 #endif