rapidio/rio_cm: use memdup_user() instead of duplicating code

Fix coccinelle warning about duplicating existing memdup_user function.

Link: http://lkml.kernel.org/r/20160811151737.20140-1-alexandre.bounine@idt.com
Link: https://lkml.org/lkml/2016/8/11/29
Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Andre van Herk <andre.van.herk@prodrive-technologies.com>
Cc: Barry Wood <barry.wood@idt.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rapidio/rio_cm.c

@@ -1841,24 +1841,19 @@ static int cm_chan_msg_send(void __user *arg)
 {
 	struct rio_cm_msg msg;
 	void *buf;
-	int ret = 0;
+	int ret;
 
 	if (copy_from_user(&msg, arg, sizeof(msg)))
 		return -EFAULT;
 	if (msg.size > RIO_MAX_MSG_SIZE)
 		return -EINVAL;
 
-	buf = kmalloc(msg.size, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
-	if (copy_from_user(buf, (void __user *)(uintptr_t)msg.msg, msg.size)) {
-		ret = -EFAULT;
-		goto out;
-	}
+	buf = memdup_user((void __user *)(uintptr_t)msg.msg, msg.size);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
 
 	ret = riocm_ch_send(msg.ch_num, buf, msg.size);
-out:
+
 	kfree(buf);
 	return ret;
 }