[LogFS] Only write journal if dirty

This prevents unnecessary journal writes.  More importantly it prevents
an oops due to a journal write on failed mount.
diff --git a/fs/logfs/readwrite.c b/fs/logfs/readwrite.c
index 1dbe6e8..7a23b3e 100644
--- a/fs/logfs/readwrite.c
+++ b/fs/logfs/readwrite.c
@@ -421,7 +421,7 @@
 
 	inode = block->inode;
 	if (inode->i_ino == LOGFS_INO_MASTER)
-		logfs_write_anchor(inode);
+		logfs_write_anchor(inode->i_sb);
 	else {
 		ret = __logfs_write_inode(inode, 0);
 		/* see indirect_write_block comment */