PCI: Add missing MEM_64 mask in pci_assign_unassigned_bridge_resources()

In 5b285415 ("PCI: Restrict 64-bit prefetchable bridge windows to
64-bit resources"), we added IORESOURCE_MEM_64 to the mask in
pci_assign_unassigned_root_bus_resources(), but not to the mask in
pci_assign_unassigned_bridge_resources().

Add IORESOURCE_MEM_64 to the pci_assign_unassigned_bridge_resources() type
mask.

Fixes: 5b285415 ("PCI: Restrict 64-bit prefetchable bridge windows to 64-bit resources")
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org	# v3.16+