ext4_utils: move sparse file pointer out of fs_info

Move the sparse file pointer out of the fs_info struct in
preparation for exporting fs_info without sparse file support.

Change-Id: I5a72147fe4fb24296e615cb82dbba91c6dc6f7f0
diff --git a/ext4_utils/extent.c b/ext4_utils/extent.c
index ce58142..aeff0f6 100644
--- a/ext4_utils/extent.c
+++ b/ext4_utils/extent.c
@@ -41,7 +41,7 @@
 
 		len = min(region_len * info.block_size, backing_len);
 
-		sparse_file_add_data(info.sparse_file, ptr, len, region_block);
+		sparse_file_add_data(ext4_sparse_file, ptr, len, region_block);
 		ptr += len;
 		backing_len -= len;
 	}
@@ -63,7 +63,7 @@
 
 		len = min(region_len * info.block_size, backing_len);
 
-		sparse_file_add_file(info.sparse_file, filename, offset, len,
+		sparse_file_add_file(ext4_sparse_file, filename, offset, len,
 				region_block);
 		offset += len;
 		backing_len -= len;
@@ -123,7 +123,7 @@
 		if (!data)
 			critical_error_errno("calloc");
 
-		sparse_file_add_data(info.sparse_file, data, info.block_size,
+		sparse_file_add_data(ext4_sparse_file, data, info.block_size,
 				extent_block);
 
 		if (((int)(info.block_size - sizeof(struct ext4_extent_header) /