x86/PCI: Remove unused alloc_pci_root_info() return value

The "info" value returned from alloc_pci_root_info() is never used, so drop
it.

[bhelgaas: commit log]
Addresses-Coverity-ID: 1222153 ("Unused value")
Link: https://lore.kernel.org/r/20210420210913.1137116-1-kw@linux.com


Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>