[fpv] Fix formal result page link

This PR fixes the FPV result summary page URL link.

Signed-off-by: Cindy Chen <chencindy@opentitan.org>
diff --git a/hw/_index.md b/hw/_index.md
index 057d383..3c43239 100644
--- a/hw/_index.md
+++ b/hw/_index.md
@@ -19,7 +19,7 @@
 ## Results of tool-flows
 
 * [DV simulation summary results, with coverage (nightly)](https://reports.opentitan.org/hw/top_earlgrey/dv/summary.html)
-* [FPV summary results (nightly)](https://reports.opentitan.org/hw/top_earlgrey/fpv/summary.html)
+* [FPV summary results (nightly)](https://reports.opentitan.org/hw/top_earlgrey/formal/summary.html)
 * [AscentLint summary results (nightly)](https://reports.opentitan.org/hw/top_earlgrey/lint/ascentlint/summary.html)
 * [Verilator lint summary results (nightly)](https://reports.opentitan.org/hw/top_earlgrey/lint/verilator/summary.html)
 * [Style lint summary results (nightly)](https://reports.opentitan.org/hw/top_earlgrey/lint/veriblelint/summary.html)