[S390] qdio: Use kstrtoul_from_user

This patch replaces the code for getting an unsigned long from a
userspace buffer by a simple call to kstroul_from_user.
This makes it easier to read and less error prone.
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Acked-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

drivers/s390/cio/qdio_debug.c

@@ -188,19 +188,13 @@ static ssize_t qperf_seq_write(struct file *file, const char __user *ubuf,
 	struct qdio_irq *irq_ptr = seq->private;
 	struct qdio_q *q;
 	unsigned long val;
-	char buf[8];
 	int ret, i;
 
 	if (!irq_ptr)
 		return 0;
-	if (count >= sizeof(buf))
-		return -EINVAL;
-	if (copy_from_user(&buf, ubuf, count))
-		return -EFAULT;
-	buf[count] = 0;
-
-	ret = strict_strtoul(buf, 10, &val);
-	if (ret < 0)
+
+	ret = kstrtoul_from_user(ubuf, count, 10, &val);
+	if (ret)
 		return ret;
 
 	switch (val) {