spi: dw: fix warning unused variable 'ret'

When CONFIG_SPI_DESIGNWARE are enabled we see the unused variable
warning in dw_spi_setup.

../drivers/spi/spi-dw.c: In function ‘dw_spi_setup’:
../drivers/spi/spi-dw.c:400:6: warning: unused variable ‘ret’ [-Wunused-variable]
  int ret;
      ^~~

Remove the unused varable.

Fixes: 9400c41e ("spi: dw: Convert to use CS GPIO descriptors")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw.c

@@ -397,7 +397,6 @@ static int dw_spi_setup(struct spi_device *spi)
 {
 	struct dw_spi_chip *chip_info = NULL;
 	struct chip_data *chip;
-	int ret;
 
 	/* Only alloc on first setup */
 	chip = spi_get_ctldata(spi);