ionic: return -EFAULT if copy_to_user() fails

The copy_to_user() function returns the number of bytes that it wasn't
able to copy.  We want to return -EFAULT to the user.

Fixes: fee6efce

 ("ionic: add hw timestamp support files")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>