ocfs2_dlmfs: Fix math error when reading LVB.

When asked for a partial read of the LVB in a dlmfs file, we can
accidentally calculate a negative count.
Reported-by: Dan Carpenter <error27@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

fs/ocfs2/dlmfs/dlmfs.c

@@ -262,7 +262,7 @@ static ssize_t dlmfs_file_read(struct file *filp,
 	if ((count + *ppos) > i_size_read(inode))
 		readlen = i_size_read(inode) - *ppos;
 	else
-		readlen = count - *ppos;
+		readlen = count;
 
 	lvb_buf = kmalloc(readlen, GFP_NOFS);
 	if (!lvb_buf)