bpf: Switch CONFIG_CFI_CLANG to CONFIG_CFI

In the Linux kernel, the following vulnerability has been resolved:

bpf: Switch CONFIG_CFI_CLANG to CONFIG_CFI

This was renamed in commit 23ef9d439769 ("kcfi: Rename CONFIG_CFI_CLANG to CONFIG_CFI") as it is now a compiler-agnostic option. Using the wrong name results in the code getting compiled out. Meaning the CFI failures for btf_dtor_kfunc_t would still trigger.