ext4: Convert bg_block_bitmap to bg_block_bitmap_lo

Convert bg_block_bitmap to bg_block_bitmap_lo
This helps in catching some BUGS due to direct
partial access of these split fields.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

fs/ext4/super.c

@@ -70,7 +70,7 @@ static void ext4_write_super_lockfs(struct super_block *sb);
 ext4_fsblk_t ext4_block_bitmap(struct super_block *sb,
 			       struct ext4_group_desc *bg)
 {
-	return le32_to_cpu(bg->bg_block_bitmap) |
+	return le32_to_cpu(bg->bg_block_bitmap_lo) |
 		(EXT4_DESC_SIZE(sb) >= EXT4_MIN_DESC_SIZE_64BIT ?
 		(ext4_fsblk_t)le32_to_cpu(bg->bg_block_bitmap_hi) << 32 : 0);
 }
@@ -94,7 +94,7 @@ ext4_fsblk_t ext4_inode_table(struct super_block *sb,
 void ext4_block_bitmap_set(struct super_block *sb,
 			   struct ext4_group_desc *bg, ext4_fsblk_t blk)
 {
-	bg->bg_block_bitmap = cpu_to_le32((u32)blk);
+	bg->bg_block_bitmap_lo = cpu_to_le32((u32)blk);
 	if (EXT4_DESC_SIZE(sb) >= EXT4_MIN_DESC_SIZE_64BIT)
 		bg->bg_block_bitmap_hi = cpu_to_le32(blk >> 32);
 }

include/linux/ext4_fs.h

@@ -105,7 +105,7 @@
  */
 struct ext4_group_desc
 {
-	__le32	bg_block_bitmap;	/* Blocks bitmap block */
+	__le32	bg_block_bitmap_lo;	/* Blocks bitmap block */
 	__le32	bg_inode_bitmap;	/* Inodes bitmap block */
 	__le32	bg_inode_table;		/* Inodes table block */
 	__le16	bg_free_blocks_count;	/* Free blocks count */