powerpc/pmac: replace current->state by set_current_state()

Use helper functions to access current->state.
Direct assignments are prone to races and therefore buggy.

current->state = TASK_RUNNING can be replaced by __set_current_state()

Thanks to Peter Zijlstra for the exact definition of the problem.
Suggested-By: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/macintosh/via-pmu.c

@@ -2112,7 +2112,7 @@ pmu_read(struct file *file, char __user *buf,
 
 	spin_lock_irqsave(&pp->lock, flags);
 	add_wait_queue(&pp->wait, &wait);
-	current->state = TASK_INTERRUPTIBLE;
+	set_current_state(TASK_INTERRUPTIBLE);
 
 	for (;;) {
 		ret = -EAGAIN;
@@ -2141,7 +2141,7 @@ pmu_read(struct file *file, char __user *buf,
 		schedule();
 		spin_lock_irqsave(&pp->lock, flags);
 	}
-	current->state = TASK_RUNNING;
+	__set_current_state(TASK_RUNNING);
 	remove_wait_queue(&pp->wait, &wait);
 	spin_unlock_irqrestore(&pp->lock, flags);