Update efs.rs

--------

Cherry picked from #160.

Author: ppdogg

easy-fs/src/efs.rs

@@ -36,7 +36,7 @@ impl EasyFileSystem {
         let data_bitmap_blocks = (data_total_blocks + 4096) / 4097;
         let data_area_blocks = data_total_blocks - data_bitmap_blocks;
         let data_bitmap = Bitmap::new(
-            (1 + inode_bitmap_blocks + inode_area_blocks) as usize,
+            (1 + inode_total_blocks) as usize,
             data_bitmap_blocks as usize,
         );
         let mut efs = Self {