pass-through: non-idempotent __insert_to_pci_slot()

pass-through: non-idempotent __insert_to_pci_slot()

As of "qemu-xen: hot-plug PCI devices at boot-time" register_real_dev()
no longer needs to call __insert_to_pci_slot() and thus there
is no need for __insert_to_pci_slot() to be idempotent.

This is because register_real_dev()'s now only has one caller,
power_on_php_slot(), which always  passes a valid e_slot to
register_real_dev().

Cc: Masaki Kanno <kanno.masaki@jp.fujitsu.com>
Cc: Edwin Zhai <edwin.zhai@intel.com>
Signed-off-by: Simon Horman <horms@verge.net.au>