spi: dw: Handle any number of gpiod CS lines

Even when configured to use only gpiod CS lines, the DW SPI controller
still expects a bit to be set in the SER register, otherwise transfers
stall. For the csgpiod case, nominate bit 0 for the job.

See: #6159

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

drivers/spi/spi-dw-core.c

@@ -98,7 +98,8 @@ void dw_spi_set_cs(struct spi_device *spi, bool enable)
 	 * support active-high or active-low CS level.
 	 */
 	if (cs_high == enable)
-		dw_writel(dws, DW_SPI_SER, BIT(spi_get_chipselect(spi, 0)));
+		dw_writel(dws, DW_SPI_SER,
+			BIT(spi_get_csgpiod(spi, 0) ? 0 : spi_get_chipselect(spi, 0)));
 	else
 		dw_writel(dws, DW_SPI_SER, 0);
 }