Documentation: devlink: add missing toc entry for etas_es58x devlink doc

toc entry is missing for etas_es58x devlink doc and triggers this warning:

Documentation/networking/devlink/etas_es58x.rst: WARNING: document isn't included in any toctree

Add the missing toc entry.

Fixes: 9f63f96aac92 ("Documentation: devlink: add devlink documentation for the etas_es58x driver")
Signed-off-by: Vincent Mailhol <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]
Reported-by: Stephen Rothwell <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Marc Kleine-Budde <[e-mail]>

Documentation/networking/devlink/index.rst

···
    :maxdepth: 1
 
    bnxt
+   etas_es58x
    hns3
    ionic
    ice