powerpc/powernv: use memdup_user

Use memdup_user() helper instead of open-coding to simplify the code.
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/opal-prd.c

@@ -241,15 +241,9 @@ static ssize_t opal_prd_write(struct file *file, const char __user *buf,
 
 	size = be16_to_cpu(hdr.size);
 
-	msg = kmalloc(size, GFP_KERNEL);
-	if (!msg)
-		return -ENOMEM;
-
-	rc = copy_from_user(msg, buf, size);
-	if (rc) {
-		size = -EFAULT;
-		goto out_free;
-	}
+	msg = memdup_user(buf, size);
+	if (IS_ERR(msg))
+		return PTR_ERR(msg);
 
 	rc = opal_prd_msg(msg);
 	if (rc) {
@@ -257,7 +251,6 @@ static ssize_t opal_prd_write(struct file *file, const char __user *buf,
 		size = -EIO;
 	}
 
-out_free:
 	kfree(msg);
 
 	return size;