perf lock contention: Fix struct rq lock access

The BPF CO-RE's ignore suffix rule requires three underscores.
Otherwise it'd fail like below:

  $ sudo perf lock contention -ab
  libbpf: prog 'collect_lock_syms': BPF program load failed: Invalid argument
  libbpf: prog 'collect_lock_syms': -- BEGIN PROG LOAD LOG --
  reg type unsupported for arg#0 function collect_lock_syms#380
  ; int BPF_PROG(collect_lock_syms)
  0: (b7) r6 = 0                        ; R6_w=0
  1: (b7) r7 = 0                        ; R7_w=0
  2: (b7) r9 = 1                        ; R9_w=1
  3: <invalid CO-RE relocation>
  failed to resolve CO-RE relocation <byte_off> [381] struct rq__new.__lock (0:0 @ offset 0)

Fixes: 0c122848

 ("perf lock contention: Support pre-5.14 kernels")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Hao Luo <haoluo@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <song@kernel.org>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20230427234833.1576130-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>