HAL_ChibiOS: fixed fast sampling on F32Lightning

this SPI bus on this board can't handle 8MHz

libraries/AP_HAL_ChibiOS/hwdef/F35Lightning/hwdef.dat

@@ -121,8 +121,8 @@ PB9 TIM4_CH4 TIM4 PWM(4) GPIO(53)
 PB0 TIM3_CH3 TIM3 PWM(5) GPIO(54)
 PB1 TIM3_CH4 TIM3 PWM(6) GPIO(55)
 
-# SPI device table
-SPIDEV mpu9250    SPI3 DEVID1 MPU9250_CS MODE3 4*MHZ 8*MHZ
+# SPI device table, note that the 9250 is not reliable at 8MHz on this board
+SPIDEV mpu9250    SPI3 DEVID1 MPU9250_CS MODE3 4*MHZ 4*MHZ
 SPIDEV bmp280     SPI3 DEVID2 BMP280_CS MODE3 1*MHZ 8*MHZ
 SPIDEV osd        SPI1 DEVID1 OSD_CS MODE0 10*MHZ 10*MHZ
 #SPIDEV sdcard     SPI2 DEVID1 SDCARD_CS MODE0 400*KHZ 25*MHZ
@@ -162,5 +162,5 @@ define HAL_BATT_CURR_PIN 12
 define HAL_BATT_VOLT_SCALE 11
 define HAL_BATT_CURR_SCALE 25
 
-# disable IMU fast sampling
-define HAL_DEFAULT_INS_FAST_SAMPLE 0
+# enable IMU fast sampling
+define HAL_DEFAULT_INS_FAST_SAMPLE 1