pcie_poll_cmd() take msecs instead of jiffies, so convert timeout to msecs.

Fixes: 40b96083 ("PCI: pciehp: Compute timeout from hotplug command start time")
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>