KVM: arm64: pmu: Drop redundant check for non-NULL kvm_pmu_events

There is an allocated and valid struct kvm_pmu_events for each cpu on the
system via DEFINE_PER_CPU(). Hence there cannot be a NULL pointer accessed
via this_cpu_ptr() in the helper kvm_get_pmu_events(). Hence non-NULL check
for pmu in such places are redundant and can be dropped.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: James Morse <james.morse@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: kvmarm@lists.linux.dev
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231012064617.897346-1-anshuman.khandual@arm.com