PCI: dra7xx: Use dw_pcie_link_up() consistently

We already use dw_pcie_link_up() once in dra7xx_pcie_establish_link(), but
we duplicate its code later.  Use dw_pcie_link_up() for consistency.  No
functional change.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Pratyush Anand <pratyush.anand@gmail.com>