dmaengine: ti: k3-udma: annotate pm function with __maybe_unused

dmaengine: ti: k3-udma: annotate pm function with __maybe_unused

We get a warning when PM is not set:

../drivers/dma/ti/k3-udma.c:5552:12: warning: 'udma_pm_resume' defined but not used [-Wunused-function]
 5552 | static int udma_pm_resume(struct device *dev)
      |            ^~~~~~~~~~~~~~
../drivers/dma/ti/k3-udma.c:5530:12: warning: 'udma_pm_suspend' defined but not used [-Wunused-function]
 5530 | static int udma_pm_suspend(struct device *dev)
      |            ^~~~~~~~~~~~~~~

Fix this by annotating pm function with __maybe_unused

Fixes: fbe05149e40b ("dmaengine: ti: k3-udma: Add system suspend/resume support")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Link: https://lore.kernel.org/r/20230516174311.117264-1-vkoul@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>