arm64: perf: fix event validation for software group leaders

commit ee7538a008a45050c8f706d38b600f55953169f9 upstream.

This is a port of c95eb3184ea1 ("ARM: 7809/1: perf: fix event validation
for software group leaders") to arm64, which fixes a panic in the arm64
perf backend found as a result of Vince's fuzzing tool.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>