[reggen] Elevate alert name check severity to error

Signed-off-by: Michael Schaffner <msf@opentitan.org>
diff --git a/util/reggen/validate.py b/util/reggen/validate.py
index 2962729..fcf3732 100644
--- a/util/reggen/validate.py
+++ b/util/reggen/validate.py
@@ -1736,11 +1736,10 @@
                 error += 1
             prefix = alert['name'].split('_')
             if prefix[0] not in ['recov', 'fatal']:
-                # TODO: to be elevated to error severity
-                log.warning(
+                log.error(
                     "{}: Alerts must be prefixed with either 'recov_' or "
                     "'fatal_'.".format(alert['name']))
-                # error += 1
+                error += 1
 
         if num_alerts != 0:
             param = ''