powerpc/pci: Fix getphbnumber() locking
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.19.256 by commit 5db5ce0f1963c6c8275719a80cb65e9c98d32726, it was introduced in version v4.19.256 by commit 205826dcac3271ab04fb97d66f1b4f8219723259. For more details please see the references link.