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 v5.4.211 by commit ccb0a42d3f40c436295e0fef57ab613ae5b925a4, it was introduced in version v5.4.211 by commit 3ec50b8a0128359ff4ad4061a75c3322d0ab6ac9. For more details please see the references link.