s390/unwind: unify task is current checks

Avoid mixture of task == NULL and task == current meaning the same
thing and simply always initialize task with current in unwind_start.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/dumpstack.c

@@ -93,8 +93,6 @@ int get_stack_info(unsigned long sp, struct task_struct *task,
 	if (!sp)
 		goto unknown;
 
-	task = task ? : current;
-
 	/* Check per-task stack */
 	if (in_task_stack(sp, task, info))
 		goto recursion_check;
@@ -128,8 +126,6 @@ void show_stack(struct task_struct *task, unsigned long *stack)
 	struct unwind_state state;
 
 	printk("Call Trace:\n");
-	if (!task)
-		task = current;
 	unwind_for_each_frame(&state, task, NULL, (unsigned long) stack)
 		printk(state.reliable ? " [<%016lx>] %pSR \n" :
 					"([<%016lx>] %pSR)\n",