idc: clear task pointer after free on prepare error

On task init failure the task allocation was freed but the pointer left
set, allowing a later free path to free it again. Clear the pointer
after freeing.

Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>

Author: lrgirdwo

src/idc/idc.c

@@ -199,6 +199,7 @@ static int idc_prepare(uint32_t comp_id)
 					    dev->ipc_config.core, 0);
 		if (ret < 0) {
 			sof_heap_free(dev->drv->user_heap, dev->task);
+			dev->task = NULL;
 			goto out;
 		}
 	}