ptp: ocp: Fix a resource leak in an error handling path

If an error occurs after a successful 'pci_ioremap_bar()' call, it must be
undone by a corresponding 'pci_iounmap()' call, as already done in the
remove function.

Fixes: a7e1abad ("ptp: Add clock driver for the OpenCompute TimeCard.")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>