spi: bcm2835: Use SPI_BPW_MASK macro for bits_per_word_mask setting

We have a SPI_BPW_MASK macro defined in spi.h, use it instead of open-coded.
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/spi/spi-bcm2835.c

@@ -314,7 +314,7 @@ static int bcm2835_spi_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, master);
 
 	master->mode_bits = BCM2835_SPI_MODE_BITS;
-	master->bits_per_word_mask = BIT(8 - 1);
+	master->bits_per_word_mask = SPI_BPW_MASK(8);
 	master->bus_num = -1;
 	master->num_chipselect = 3;
 	master->transfer_one_message = bcm2835_spi_transfer_one;