misc: pci_endpoint_test: Ensure relationship between miscdev and PCI

Set the parent pointer of the misc device to ensure a relationship
between PCI and misc dev. That way it is possible to see in
/sys/class/misc/ which pci_endpoint_test instance serves what
PCI device.

Signed-off-by: Richard Weinberger <richard@nod.at>
Link: https://lore.kernel.org/r/20210706154310.26773-1-richard@nod.at


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>