dmaengine :ipu: change ipu_irq_handler() to remove compile warning

Change ipu_irq_handler() to avoid gcc warning:

drivers/dma/ipu/ipu_irq.c:305:4: warning: 'irq' may be used
uninitialized in this function [-Wmaybe-uninitialized]
    generic_handle_irq(irq);

Signed-off-by: yalin wang <yalin.wang2010@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>