perf mem-events: Avoid uninitialized read

stable inclusion
from stable-v6.6.2
commit 650b41987aaed10307eab16c9a2c638dc5bf8758
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8IW7G

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=650b41987aaed10307eab16c9a2c638dc5bf8758



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[ Upstream commit 85f73c377b2ac9988a204b119aebb33ca5c60083 ]

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.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>