ocfs2: validate l_tree_depth to avoid out-of-bounds access

In the Linux kernel, the following vulnerability has been resolved:

ocfs2: validate l_tree_depth to avoid out-of-bounds access

The l_tree_depth field is 16-bit (__le16), but the actual maximum depth is

limited to OCFS2_MAX_PATH_DEPTH.

Add a check to prevent out-of-bounds access if l_tree_depth has an invalid

value, which may occur when reading from a corrupted mounted disk [1].