libbpf: Fix off-by-one bug in bpf_core_apply_relo()

Fix instruction index validity check which has off-by-one error.

Fixes: 3ee4f53 ("libbpf: Split bpf_core_apply_relo() into bpf_program independent helper.")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211025224531.1088894-2-andrii@kernel.org

tools/lib/bpf/libbpf.c

@@ -5405,7 +5405,7 @@ static int bpf_core_apply_relo(struct bpf_program *prog,
 	 * relocated, so it's enough to just subtract in-section offset
 	 */
 	insn_idx = insn_idx - prog->sec_insn_off;
-	if (insn_idx > prog->insns_cnt)
+	if (insn_idx >= prog->insns_cnt)
 		return -EINVAL;
 	insn = &prog->insns[insn_idx];