[media] m2m-deinterlace: fix allocated struct type

'xt' points to a dma_interleaved_template and not a dma_async_tx_descriptor.

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>