SKR-PRO: Fix FAN0 PWM speed with Heater2 (#15889)

buildroot/share/PlatformIO/variants/BIGTREE_SKR_PRO_1v1/PeripheralPins.c

   {PD_14, TIM4,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM4, 3, 0)}, // TIM4_CH3    HEATER1
   {PB_0,  TIM3,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 3, 0)}, // TIM3_CH3    HEATER2
   {PD_12, TIM4,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM4, 1, 0)}, // TIM4_CH1    BED
-  {PC_8,  TIM3,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 3, 0)}, // TIM3_CH3    FAN0
+  {PC_8,  TIM8,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM8, 3, 0)}, // TIM8_CH3    FAN0
   {PE_5,  TIM9,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM9, 1, 0)}, // TIM9_CH1    FAN1
   {PE_6,  TIM9,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM9, 2, 0)}, // TIM9_CH2    FAN2
   {PC_9,  TIM8,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM8, 4, 0)}, // TIM8_CH4    EXTENSION1-4
   //{PC_6,  TIM8,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM8, 1, 0)}, // TIM8_CH1
   //{PC_7,  TIM3,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 2, 0)}, // TIM3_CH2
   //{PC_7,  TIM8,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM8, 2, 0)}, // TIM8_CH2
-  //{PC_8,  TIM8,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM8, 3, 0)}, // TIM8_CH3
+  //{PC_8,  TIM3,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 3, 0)}, // TIM3_CH3
   //{PC_9,  TIM3,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 4, 0)}, // TIM3_CH4
   //{PD_13, TIM4,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM4, 2, 0)}, // TIM4_CH2
   //{PD_15, TIM4,   STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM4, 4, 0)}, // TIM4_CH4