fix a clang warning

Author: Rao Meng

fmtlog-inl.h

@@ -372,7 +372,7 @@ class fmtlogDetailT
     hour.fromi(h);
     setArgVal<14>(info.getBase());
     setArgVal<15>(info.getLocation());
-    logLevel = "DBG INF WRN ERR OFF" + (info.logLevel << 2);
+    logLevel = (const char*)"DBG INF WRN ERR OFF" + (info.logLevel << 2);
 
     size_t headerPos = membuf.size();
     fmt::detail::vformat_to(membuf, headerPattern, fmt::basic_format_args(args.data(), parttenArgSize));