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>
diff --git a/include/linux/ext4_fs.h b/include/linux/ext4_fs.h
index 46b304d..1dab984 100644
--- a/include/linux/ext4_fs.h
+++ b/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 */