Fix USEABLE_HARDWARE_PWM

Marlin/src/HAL/HAL_AVR/fastio_AVR.h

   #error "unknown CPU"
 #endif
 
-#define USEABLE_HARDWARE_PWM(P) (PWM_PIN(P) && !PWM_CHK(p))
+#define USEABLE_HARDWARE_PWM(P) (PWM_PIN(P) && !PWM_CHK(P))