NodeDB: Change pointer to const for mesh node retrieval in loadFromDisk (#11315)

Addresses cppcheck
src/mesh/NodeDB.cpp:2431: [low:style] Variable 'us' can be declared as pointer to const [constVariablePointer]

src/mesh/NodeDB.cpp

@@ -2428,7 +2428,7 @@ void NodeDB::loadFromDisk()
         installDefaultDeviceState();
 
         // Attempt recovery of owner fields from our own NodeDB entry if available.
-        meshtastic_NodeInfoLite *us = getMeshNode(getNodeNum());
+        const meshtastic_NodeInfoLite *us = getMeshNode(getNodeNum());
         if (nodeInfoLiteHasUser(us)) {
             LOG_WARN("Restoring owner fields (long_name/short_name/is_licensed/is_unmessagable) from NodeDB for our node 0x%08x",
                      us->num);