ptp_ocp: do not call pci_set_drvdata(pdev, NULL)

Cleaning up driver data is actually already handled by driver core,
so there is no need to do it manually.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Vadim Fedorenko <vfedorenko@novek.ru>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>