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 v5.10.138 by commit a868f771ee41c97a25a04b8c632a7f06689b307b, it was introduced in version v5.10.137 by commit 47a8fe1b154aa6d836582365b1c70684af8597e4. For more details please see the references link.