dmaengine: pl330: fix the pl330 build after cookie cleanup

drivers/dma/pl330.c: In function 'pl330_control':
drivers/dma/pl330.c:342: error: 'struct dma_pl330_chan' has no member named
'completed'

Reported by: Jassi Brar <jassisinghbrar@gmail.com>
Suggested by: Jassi Brar <jassisinghbrar@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>