riscv, bpf: Fix possible infinite tailcall when CONFIG_CFI_CLANG is enabled

When CONFIG_CFI_CLANG is enabled, the number of prologue instructions
skipped by tailcall needs to include the kcfi instruction, otherwise the
TCC will be initialized every tailcall is called, which may result in
infinite tailcalls.

Fixes: e63985ec ("bpf, riscv64/cfi: Support kCFI + BPF on riscv64")
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Acked-by: Björn Töpel <bjorn@kernel.org>
Link: https://lore.kernel.org/r/20241008124544.171161-1-pulehui@huaweicloud.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>