DataFlash: allow startup with no microSD

this allows logging to work with insert after boot

libraries/DataFlash/DataFlash_File.cpp

@@ -134,7 +134,6 @@ void DataFlash_File::Init()
     }
     if (ret == -1) {
         printf("Failed to create log directory %s : %s\n", _log_directory, strerror(errno));
-        return;
     }
 
     // determine and limit file backend buffersize