Fix handling of ssl_key_handler for WebUI

The previous commit 90cd2e1 [1] causes WebUI to fail to load and
connect.  It is because a global static var (`hasWebuiRoute`) is
instantiated per compile unit and it ends up causing the inconsistency
of the value of it.

Tested:
- Verify WebUI to load successful
- Redfish Service Validator passes

[1] https://github.com/openbmc/bmcweb/commit/90cd2e1d2e2228b0c575c9a3b6b2dc75eac9eb68

Change-Id: I09c3a9a831528e25c09299b0ee15993974d94d88
Signed-off-by: Myung Bae <myungbae@us.ibm.com>
diff --git a/include/webassets.hpp b/include/webassets.hpp
index aa57230..baa16c4 100644
--- a/include/webassets.hpp
+++ b/include/webassets.hpp
@@ -216,7 +216,7 @@
 
     if (webpath == "/")
     {
-        forward_unauthorized::hasWebuiRoute = true;
+        forward_unauthorized::hasWebuiRoute() = true;
     }
 
     app.routeDynamic(webpath)(