PCI: Keep original resource if we fail to expand it

If we have space assigned to a resource, we try to expand the resource
(e.g., to accommodate SR-IOV resources), and the expansion attempt fails,
we should keep the original assignment.

After bd064f0a ("PCI: Mark resources as IORESOURCE_UNSET if we can't
assign them"), we left the resource marked IORESOURCE_UNSET when the
expansion failed, even if it had originally been set.  That caused errors
like this:

  pci 0003:00:00.0: can't enable device: BAR 15 [mem size 0x0c000000 64bit pref] not assigned
  pci 0003:00:00.0: Error enabling bridge (-22), continuing

Fix this by restoring the original flags when reassignment fails.

[bhelgaas: reworked to simplify, changelog]
Fixes: bd064f0a ("PCI: Mark resources as IORESOURCE_UNSET if we can't assign them")
Signed-off-by: Guo Chao <yan@linux.vnet.ibm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org	# v3.15+