posix-cpu-timers: Fix pid refcount leak in do_cpu_nanosleep() error path

In the Linux kernel, the following vulnerability has been resolved: posix-cpu-timers: Fix pid refcount leak in do_cpu_nanosleep() error path In do_cpu_nanosleep(), posix_cpu_timer_create() takes a pid reference via get_pid() and stores it in timer.it.cpu.pid. If the subsequent posix_cpu_timer_set() call fails, the function returns immediately without calling posix_cpu_timer_del() to release the pid reference, causing a leak. Fix it by calling posix_cpu_timer_del() before the unlock-and-return on the error path, consistent with the other exit paths in the same function.