PCI: pciehp: Make check_link_active() non-static

check_link_active() functionality needs to be used by subsequent patches
(that introduce link state change based hotplug). Thus make the function
non-static, and rename it to pciehp_check_link_active() so as to be
consistent with other non-static functions.

Signed-off-by: Rajat Jain <rajatxjain@gmail.com>
Signed-off-by: Rajat Jain <rajatjain@juniper.net>
Signed-off-by: Guenter Roeck <groeck@juniper.net>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>