dmaengine: at_xdmac: fix compilation warning

Fixed "unused variable 'atmel_xdmac_dev_pm_ops'" compilation warning
when CONFIG_PM is not defined.

Fixes: 8e0c7e48 ("dmaengine: at_xdmac: use pm_ptr()")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20211025074002.722504-1-claudiu.beznea@microchip.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/at_xdmac.c

@@ -2207,7 +2207,7 @@ static int at_xdmac_remove(struct platform_device *pdev)
 	return 0;
 }
 
-static const struct dev_pm_ops atmel_xdmac_dev_pm_ops = {
+static const struct dev_pm_ops __maybe_unused atmel_xdmac_dev_pm_ops = {
 	.prepare	= atmel_xdmac_prepare,
 	SET_LATE_SYSTEM_SLEEP_PM_OPS(atmel_xdmac_suspend, atmel_xdmac_resume)
 };