Fix uninitialized muxes for dimmer lights (#356)

code/espurna/libs/pwm.h

@@ -9,7 +9,7 @@
  /*NOTE!!  : DO NOT CHANGE THIS FILE*/
 
  /*SUPPORT UP TO 8 PWM CHANNEL*/
-#define PWM_CHANNEL_NUM_MAX 8 
+//#define PWM_CHANNEL_NUM_MAX 8 
 
 struct pwm_param {
     uint32 period;

code/espurna/light.ino

@@ -13,6 +13,7 @@ Copyright (C) 2016-2017 by Xose Pérez <xose dot perez at gmail dot com>
 #include <vector>
 
 #if LIGHT_PROVIDER == LIGHT_PROVIDER_DIMMER
+#define PWM_CHANNEL_NUM_MAX LIGHT_CHANNELS
 extern "C" {
     #include "libs/pwm.h"
 }