selftests/bpf: Fix array bounds warning in jit_disasm_helpers

selftests/bpf: Fix array bounds warning in jit_disasm_helpers

Compiler cannot infer upper bound for labels.cnt and warns about
potential buffer overflow in snprintf. Add an explicit bounds
check (... && i < MAX_LOCAL_LABELS) in the loop condition to fix the
warning.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Link: https://lore.kernel.org/r/20260223190736.649171-18-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>