genirq/proc: Return proper error code when irq_set_affinity() fails

write_irq_affinity() returns the number of written bytes, which means
success, unconditionally whether the actual irq_set_affinity() call
succeeded or not.

Add proper error handling and pass the error code returned from
irq_set_affinity() back to user space in case of failure.

[ tglx: Fixed coding style and massaged changelog ]
Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
Cc: zhong.weidong@zte.com.cn
Link: https://lkml.kernel.org/r/1510106103-184761-1-git-send-email-wen.yang99@zte.com.cn

kernel/irq/proc.c

@@ -154,7 +154,8 @@ static ssize_t write_irq_affinity(int type, struct file *file,
 		 */
 		err = irq_select_affinity_usr(irq) ? -EINVAL : count;
 	} else {
-		irq_set_affinity(irq, new_value);
+		err = irq_set_affinity(irq, new_value);
+		if (!err)
 			err = count;
 	}