spi: spi-mem: fallback to using transfers when CS gpios are used

Devices with chip selects driven via GPIO are not compatible with the
spi-mem operations. Fallback to using standard spi transfers when the
device is connected with a gpio CS.
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Link: https://lore.kernel.org/r/20191107044235.4864-3-chris.packham@alliedtelesis.co.nzSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-mem.c

@@ -286,7 +286,7 @@ int spi_mem_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
 	if (!spi_mem_internal_supports_op(mem, op))
 		return -ENOTSUPP;
 
-	if (ctlr->mem_ops) {
+	if (ctlr->mem_ops && !mem->spi->cs_gpiod) {
 		ret = spi_mem_access_start(mem);
 		if (ret)
 			return ret;