spi/au1550_spi: fix setupxfer not to override cfg with zeros

fix setupxfer() not to override generic configuration of speed_hz
and bits_per_word with zeros
Signed-off-by: NJan Nikitenko <jan.nikitenko@gmail.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

drivers/spi/au1550_spi.c

@@ -237,8 +237,14 @@ static int au1550_spi_setupxfer(struct spi_device *spi, struct spi_transfer *t)
 	unsigned bpw, hz;
 	u32 cfg, stat;
 
-	bpw = t ? t->bits_per_word : spi->bits_per_word;
-	hz = t ? t->speed_hz : spi->max_speed_hz;
+	bpw = spi->bits_per_word;
+	hz = spi->max_speed_hz;
+	if (t) {
+		if (t->bits_per_word)
+			bpw = t->bits_per_word;
+		if (t->speed_hz)
+			hz = t->speed_hz;
+	}
 
 	if (bpw < 4 || bpw > 24) {
 		dev_err(&spi->dev, "setupxfer: invalid bits_per_word=%d\n",