spi: armada-3700: Replaced raw values for nbits by the SPI macros

Currently, function a3700_spi_pin_mode_set() configures the SPI transfer
mode according to the value passed as second argument. This value is
detected using the raw values from a switch case.

This commit replaces these raw values by the corresponding macro
constants in linux/spi/spi.h

Signed-off-by: Romain Perier <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-armada-3700.c

···
 	val &= ~(A3700_SPI_DATA_PIN0 | A3700_SPI_DATA_PIN1);
 
 	switch (pin_mode) {
-	case 1:
+	case SPI_NBITS_SINGLE:
 		break;
-	case 2:
+	case SPI_NBITS_DUAL:
 		val |= A3700_SPI_DATA_PIN0;
 		break;
-	case 4:
+	case SPI_NBITS_QUAD:
 		val |= A3700_SPI_DATA_PIN1;
 		break;
 	default: