perf mem-events: Avoid uninitialized read

pmu should be initialized to NULL before perf_pmus__scan loop. Fix and
shrink the scope of pmu at the same time. Issue detected by clang-tidy.

Fixes: 5752c20f ("perf mem: Scan all PMUs instead of just core ones")
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Yang Jihong <yangjihong1@huawei.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: llvm@lists.linux.dev
Cc: Ming Wang <wangming01@loongson.cn>
Cc: Tom Rix <trix@redhat.com>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20231009183920.200859-10-irogers@google.comSigned-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/util/mem-events.c

@@ -185,7 +185,6 @@ int perf_mem_events__record_args(const char **rec_argv, int *argv_nr,
 {
 	int i = *argv_nr, k = 0;
 	struct perf_mem_event *e;
-	struct perf_pmu *pmu;
 
 	for (int j = 0; j < PERF_MEM_EVENTS__MAX; j++) {
 		e = perf_mem_events__ptr(j);
@@ -202,6 +201,8 @@ int perf_mem_events__record_args(const char **rec_argv, int *argv_nr,
 			rec_argv[i++] = "-e";
 			rec_argv[i++] = perf_mem_events__name(j, NULL);
 		} else {
+			struct perf_pmu *pmu = NULL;
+
 			if (!e->supported) {
 				perf_mem_events__print_unsupport_hybrid(e, j);
 				return -1;