spi: spi-synquacer: fix set_cs handling

When the slave chip select is deasserted, DMSTOP bit
must be set.

Fixes: b0823ee35c ("spi: Add spi driver for Socionext SynQuacer platform")
Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210201073109.9036-1-jassisinghbrar@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-synquacer.c

@@ -490,6 +490,10 @@ static void synquacer_spi_set_cs(struct spi_device *spi, bool enable)
 	val &= ~(SYNQUACER_HSSPI_DMPSEL_CS_MASK <<
 		 SYNQUACER_HSSPI_DMPSEL_CS_SHIFT);
 	val |= spi->chip_select << SYNQUACER_HSSPI_DMPSEL_CS_SHIFT;
+
+	if (!enable)
+		val |= SYNQUACER_HSSPI_DMSTOP_STOP;
+
 	writel(val, sspi->regs + SYNQUACER_HSSPI_REG_DMSTART);
 }