pcie_port_device_remove currently calls the remove method of port
drivers twice.  Ouch!

We are calling device_for_each_child multiple times for no apparent
reason.

So make it simple. Place put_device and device_unregister into
remove_iter, and throw out the rest.  Only call device_for_each_child
once.

The code is simpler and actually works!
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>