iio: common: ssp_sensors: Protect PM-only functions to kill warning

If CONFIG_PM_SLEEP=n:

    drivers/iio/common/ssp_sensors/ssp_dev.c:644: warning: ‘ssp_suspend’ defined but not used
    drivers/iio/common/ssp_sensors/ssp_dev.c:669: warning: ‘ssp_resume’ defined but not used

Protect the unused functions by #ifdef CONFIG_PM_SLEEP to fix this.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Karol Wrona <k.wrona@samsung.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/common/ssp_sensors/ssp_dev.c

@@ -640,6 +640,7 @@ static int ssp_remove(struct spi_device *spi)
 	return 0;
 }
 
+#ifdef CONFIG_PM_SLEEP
 static int ssp_suspend(struct device *dev)
 {
 	int ret;
@@ -688,6 +689,7 @@ static int ssp_resume(struct device *dev)
 
 	return 0;
 }
+#endif /* CONFIG_PM_SLEEP */
 
 static const struct dev_pm_ops ssp_pm_ops = {
 	SET_SYSTEM_SLEEP_PM_OPS(ssp_suspend, ssp_resume)