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/make_ext4fs.c b/ext4_utils/make_ext4fs.c
index c2a2665..2250241 100644
--- a/ext4_utils/make_ext4fs.c
+++ b/ext4_utils/make_ext4fs.c
@@ -362,9 +362,9 @@
     memset(&info, 0, sizeof(info));
     memset(&aux_info, 0, sizeof(aux_info));
 
-    if (info.sparse_file) {
-        sparse_file_destroy(info.sparse_file);
-        info.sparse_file = NULL;
+    if (ext4_sparse_file) {
+        sparse_file_destroy(ext4_sparse_file);
+        ext4_sparse_file = NULL;
     }
 }
 
@@ -545,7 +545,7 @@
 	printf("    Block groups: %d\n", aux_info.groups);
 	printf("    Reserved block group size: %d\n", info.bg_desc_reserve_blocks);
 
-	info.sparse_file = sparse_file_new(info.block_size, info.len);
+	ext4_sparse_file = sparse_file_new(info.block_size, info.len);
 
 	block_allocator_init();
 
@@ -607,8 +607,8 @@
 
 	write_ext4_image(fd, gzip, sparse, crc);
 
-	sparse_file_destroy(info.sparse_file);
-	info.sparse_file = NULL;
+	sparse_file_destroy(ext4_sparse_file);
+	ext4_sparse_file = NULL;
 
 	free(mountpoint);
 	free(directory);