Documentation: trace: Reduce toctree depth

Reduce toctree depth from 2 to 1 so that only docs titles are listed
in the toctree.

Signed-off-by: Purva Yeshi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
[Bagas: massage commit message]
Signed-off-by: Bagas Sanjaya <[e-mail]>
Acked-by: Steven Rostedt (Google) <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/trace/index.rst

···
 ==========================
 
 .. toctree::
-   :maxdepth: 2
+   :maxdepth: 1
 
    ftrace-design
    tracepoint-analysis