x86/PCI: add spinlock held check to 'pcibios_fwaddrmap_lookup()'
'pcibios_fwaddrmap_lookup()' is used to maintain FW-assigned BIOS BAR
values for reinstatement when normal resource assignment attempts
fail and must be called with the 'pcibios_fwaddrmap_lock' spinlock
held.
This patch adds a WARN_ON notification if the spinlock is not currently
held by the caller.