Change default SPI mode to 0 to match datasheet

"Data is latched on the rising edge of SCLK" - this is CPHA = 0. It's not clear what CPOL is but mode 3 is not CPHA = 1 which causes SPI to not work on some platforms (Artemis).

Author: Nathan Seidle

src/ICM_20948.h

@@ -140,7 +140,7 @@ class ICM_20948_I2C : public ICM_20948
 // SPI
 #define ICM_20948_SPI_DEFAULT_FREQ 7000000
 #define ICM_20948_SPI_DEFAULT_ORDER MSBFIRST
-#define ICM_20948_SPI_DEFAULT_MODE SPI_MODE3
+#define ICM_20948_SPI_DEFAULT_MODE SPI_MODE0
 
 // Forward declarations of SPIClass and SPI for board/variant combinations that don't have a default 'SPI'
 class SPIClass;