UPSTREAM: perf/core: Fix potential NULL deref

Smatch is awesome.

Fixes: 32671e37 ("perf: Disallow mis-matched inherited group reads")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Change-Id: I7691e0aaaee70f1d0db3d1e33983d7236f72ed0c
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit a71ef314)
Bug: 361274701
Bug: 361674357
Signed-off-by: 杨辉 <yanghui10@xiaomi.corp-partner.google.com>