spi/pxa2xx: fix compilation warning when !CONFIG_PM_SLEEP

CONFIG_PM will be set if either or both CONFIG_PM_SLEEP and
CONFIG_PM_RUNTIME is set. Compiling the driver with !CONFIG_PM_SLEEP causes
following compilation warning:

drivers/spi/spi-pxa2xx.c:1270:12: warning: ‘pxa2xx_spi_suspend’ defined but not used [-Wunused-function]

Fix this by using CONFIG_PM_SLEEP instead.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/spi/spi-pxa2xx.c

@@ -1264,7 +1264,7 @@ static void pxa2xx_spi_shutdown(struct platform_device *pdev)
 		dev_err(&pdev->dev, "shutdown failed with %d\n", status);
 }
 
-#ifdef CONFIG_PM
+#ifdef CONFIG_PM_SLEEP
 static int pxa2xx_spi_suspend(struct device *dev)
 {
 	struct driver_data *drv_data = dev_get_drvdata(dev);