vfio: simplify kmalloc+copy_from_user to memdup_user

			    hdr.count > vfio_pci_get_irq_count(vdev, hdr.index))

				return -EINVAL;

			data = kmalloc(hdr.count * size, GFP_KERNEL);

			if (!data)

				return -ENOMEM;

			if (copy_from_user(data, (void __user *)(arg + minsz),

					   hdr.count * size)) {

				kfree(data);

				return -EFAULT;

			}

			data = memdup_user((void __user *)(arg + minsz),

					   hdr.count * size);

			if (IS_ERR(data))

				return PTR_ERR(data);

		}

		mutex_lock(&vdev->igate);