fixup e305493b -DWITH_DBUG_TRACE=ON

ha_innobase::can_switch_engines(): Use DBUG_RETURN instead of return
to match the DBUG_ENTER. This fixes a bootstrap failure of debug builds
using the default setting -DWITH_DBUG_TRACE=ON.

storage/innobase/handler/ha_innodb.cc

@@ -15294,8 +15294,8 @@ bool ha_innobase::can_switch_engines()
 {
   DBUG_ENTER("ha_innobase::can_switch_engines");
   update_thd();
-  return m_prebuilt->table->foreign_set.empty() &&
-    m_prebuilt->table->referenced_set.empty();
+  DBUG_RETURN(m_prebuilt->table->foreign_set.empty() &&
+              m_prebuilt->table->referenced_set.empty());
 }
 
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