Plane: fixed two build warnings with clang

ArduPlane/Parameters.cpp

@@ -1277,6 +1277,6 @@ void Plane::load_parameters(void)
         // Load all auto-loaded EEPROM variables
         AP_Param::load_all();
         AP_Param::convert_old_parameters(&conversion_table[0], ARRAY_SIZE(conversion_table));
-        cliSerial->printf("load_all took %uus\n", micros() - before);
+        cliSerial->printf("load_all took %uus\n", (unsigned)(micros() - before));
     }
 }

ArduPlane/system.cpp

@@ -81,7 +81,7 @@ void Plane::init_ardupilot()
 
     cliSerial->printf("\n\nInit " FIRMWARE_STRING
                          "\n\nFree RAM: %u\n",
-                        hal.util->available_memory());
+                      (unsigned)hal.util->available_memory());
 
 
     //