If we pass ERR_PTR(-EFAULT) to kfree() then it's going to oops.

Fixes: 2ece068e ('ptp: use memdup_user().')
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Acked-by: NRichard Cochran <richardcochran@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>