UPSTREAM: perf/core: Fix potential NULL deref

commit a71ef314 upstream.

Smatch is awesome.

Fixes: 32671e37 ("perf: Disallow mis-matched inherited group reads")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 0258ca32)
Change-Id: I6d2005d6c186cfc7ff41ed2615e37ee9f01da6a5
Bug: 442358987
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>