[source] ar71xx: fix RB4xx CPLD SPI device mode setup

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/889272d92db689fd9c910243635e44c9d8323095

commit 889272d92db689fd9c910243635e44c9d8323095
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Wed Jan 11 10:42:04 2017 +0100

    ar71xx: fix RB4xx CPLD SPI device mode setup
    
    Commit af79fdbe4af3 changed the code to use tx_nbits for dual SPI tx
    transfers, however the SPI stack only allows this when the device mode
    includes the relevant bit as well
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 target/linux/ar71xx/files/drivers/spi/spi-rb4xx-cpld.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/linux/ar71xx/files/drivers/spi/spi-rb4xx-cpld.c b/target/linux/ar71xx/files/drivers/spi/spi-rb4xx-cpld.c
index f6ec350..0534c7c 100644
--- a/target/linux/ar71xx/files/drivers/spi/spi-rb4xx-cpld.c
+++ b/target/linux/ar71xx/files/drivers/spi/spi-rb4xx-cpld.c
@@ -279,7 +279,7 @@ static int rb4xx_cpld_probe(struct spi_device *spi)
 	cpld->spi = spi_dev_get(spi);
 	dev_set_drvdata(&spi->dev, cpld);
 
-	spi->mode = SPI_MODE_0;
+	spi->mode = SPI_MODE_0 | SPI_TX_DUAL;
 	spi->bits_per_word = 8;
 	err = spi_setup(spi);
 	if (err) {