kernel: ftrace: Fix NULL pointer dereference in is_ftrace_trampoline when ftrace is dead

In the Linux kernel, the following vulnerability has been resolved: ftrace: Fix NULL pointer dereference in isftracetrampoline when ftrace is dead ftracestartup does not remove ops from ftraceopslist when ftracestartupenable fails: registerftracefunction ftracestartup registerftracefunction...