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.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>