Fixes the following cppcheck issues:
examples/SecretKnockSensor/SecretKnockSensor.ino
305 variableScope 398 style
The scope of the variable 'timeDiff' can be reduced.
examples/SensebenderGatewaySerial/SensebenderGatewaySerial.ino
127 variableScope 398 style
The scope of the variable 'led_state' can be reduced.