tools/power/x86/intel-speed-select: Harden daemon pidfile open

In the Linux kernel, the following vulnerability has been resolved: tools/power/x86/intel-speed-select: Harden daemon pidfile open Avoid symlink-based pidfile clobbering by opening the pidfile with O_NOFOLLOW and validating it with fstat() before locking/writing. The daemon currently uses a fixed pidfile path under /tmp. A local unprivileged user can pre-create a symlink at that path and cause a root-run daemon instance to write into an attacker-chosen file.