HAL_ChibiOS: adjust SPI clock rates on FMUv4

this prevents some timing errors on the IMUs

libraries/AP_HAL_ChibiOS/hwdef/fmuv4/hwdef.dat

@@ -143,8 +143,8 @@ PE15 MAG_CS CS
 # of ArduPilot so users don't need to re-do their accel and compass calibrations
 # when moving to ChibiOS
 SPIDEV ms5611_int  SPI2 DEVID3  BARO_CS    MODE3  20*MHZ  20*MHZ
-SPIDEV mpu9250     SPI1 DEVID4  MPU9250_CS MODE3   1*MHZ   8*MHZ
-SPIDEV icm20608    SPI1 DEVID6  20608_CS   MODE3   1*MHZ   8*MHZ
+SPIDEV mpu9250     SPI1 DEVID4  MPU9250_CS MODE3   2*MHZ   4*MHZ
+SPIDEV icm20608    SPI1 DEVID6  20608_CS   MODE3   2*MHZ   8*MHZ
 SPIDEV hmc5843     SPI1 DEVID5  MAG_CS     MODE3  11*MHZ  11*MHZ
 SPIDEV lis3mdl     SPI1 DEVID5  MAG_CS     MODE3 500*KHZ 500*KHZ
 SPIDEV ramtron     SPI2 DEVID10 FRAM_CS    MODE3   8*MHZ   8*MHZ