Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
index 1f3755b..ddf28ec 100644
--- a/fs/btrfs/export.c
+++ b/fs/btrfs/export.c
@@ -33,7 +33,7 @@
 	type = FILEID_BTRFS_WITHOUT_PARENT;
 
 	fid->objectid = btrfs_ino(BTRFS_I(inode));
-	fid->root_objectid = BTRFS_I(inode)->root->objectid;
+	fid->root_objectid = BTRFS_I(inode)->root->root_key.objectid;
 	fid->gen = inode->i_generation;
 
 	if (parent) {
@@ -41,7 +41,7 @@
 
 		fid->parent_objectid = BTRFS_I(parent)->location.objectid;
 		fid->parent_gen = parent->i_generation;
-		parent_root_id = BTRFS_I(parent)->root->objectid;
+		parent_root_id = BTRFS_I(parent)->root->root_key.objectid;
 
 		if (parent_root_id != fid->root_objectid) {
 			fid->parent_root_objectid = parent_root_id;