spidev: Switch to use spi_get_csgpiod()

spidev_ioctl() checks if there is an SPI chip select is driven by GPIO.
Instead of current code, we can call spi_get_csgpiod().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Link: https://lore.kernel.org/r/20230824162209.2890440-3-andriy.shevchenko@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>