one more minor fix to use constant rather than hard coding value in pwm fade test
one more minor fix to use constant rather than hard coding value in pwm fade test

Cerberus98/lightshowpi,bradowen2011/lightshowpi,wheeldog515/lightshowPi,Cerberus98/lightshowpi,wheeldog515/lightshowPi,bradowen2011/lightshowpi