KVM: arm/arm64: vgic-its: Check result of allocation before use

KVM: arm/arm64: vgic-its: Check result of allocation before use

commit 686f294f2f1ae40705283dd413ca1e4c14f20f93 upstream.

We miss a test against NULL after allocation.

Fixes: 6d03a68f8054 ("KVM: arm64: vgic-its: Turn device_id validation into generic ID validation")
Reported-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>