PCI: xgene: Removed unused ".bus_shift" initialisers from pci-xgene.c

Removed unused ".bus_shift" initialisers from pci-xgene.c as
xgene_pcie_map_bus() did not use these.

Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20201129230743.3006978-6-kw@linux.com


Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>