GSD-2022-1005502 powerpc/pci: Fix get_phb_number() locking

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 v5.15.63 by commit 1d9e75c3d8cdf7c96a94cb77450d4ee070279e6...