dmaengine: ipu: use return value of request_irq

Commit - 653e67f7: "dmaengine: inherit debug settings from the subsystem
for subdirectories" introduced debug option for subdirectories too
This exposed issue with ipu driver not using return value

For now just warn users about it

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>