s390/pci: Fix duplicate pci_dev_put() in disable_slot() when PF has child VFs

With commit bcb5d6c7 ("s390/pci: introduce lock to synchronize state
of zpci_dev's") the code to ignore power off of a PF that has child VFs
was changed from a direct return to a goto to the unlock and
pci_dev_put() section. The change however left the existing pci_dev_put()
untouched resulting in a doubple put. This can subsequently cause a use
after free if the struct pci_dev is released in an unexpected state.
Fix this by removing the extra pci_dev_put().

Cc: stable@vger.kernel.org
Fixes: bcb5d6c7 ("s390/pci: introduce lock to synchronize state of zpci_dev's")
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Reviewed-by: Gerd Bayer <gbayer@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>