staging: mt7621-pci: use PCIE_PORT_LINKUP instead of hardcode value

PCIE_PORT_LINKUP is defined and can be used to check if link is up
for each controller. Use it instead of use a hardcode value.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>