PCI: keystone-dw: Remove unused ks_pcie, pci variables

The ks_pcie and pci variables in ks_dw_pcie_msi_irq_mask() and
ks_dw_pcie_msi_irq_unmask() are never used.  Remove them.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>