'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.
Signed-off-by: NMyron Stowe <myron.stowe@redhat.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>