systemc: Add a missing "const" on one of the sc_event operators.

Change-Id: I073ccb0f2c6d1bfebadb95869d6acf7f4ce565af
Reviewed-on: https://gem5-review.googlesource.com/c/14135
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>
diff --git a/src/systemc/core/sc_event.cc b/src/systemc/core/sc_event.cc
index 75d5c89..6774254 100644
--- a/src/systemc/core/sc_event.cc
+++ b/src/systemc/core/sc_event.cc
@@ -99,7 +99,7 @@
 }
 
 sc_event_and_expr
-sc_event_and_list::operator & (const sc_event_and_list &eal)
+sc_event_and_list::operator & (const sc_event_and_list &eal) const
 {
     sc_event_and_expr expr;
     expr.insert(*this);
diff --git a/src/systemc/ext/core/sc_event.hh b/src/systemc/ext/core/sc_event.hh
index e2164f4..7925e08 100644
--- a/src/systemc/ext/core/sc_event.hh
+++ b/src/systemc/ext/core/sc_event.hh
@@ -76,7 +76,7 @@
     sc_event_and_list &operator &= (const sc_event_and_list &);
 
     sc_event_and_expr operator & (const sc_event &) const;
-    sc_event_and_expr operator & (const sc_event_and_list &);
+    sc_event_and_expr operator & (const sc_event_and_list &) const;
 
   private:
     friend class sc_event_and_expr;