Documentation: Fix too short title underline in ipa.rst

Sphinx build is broken from the commit (0906ddb2) because a
title underline is too short. This fixed the breakage.

Fixes: 0906ddb2681a ("Documentation: Add IPA writers guide")
Signed-off-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
1 file changed