KVM: selftests: Assert that MPIDR_EL1 is unchanged across vCPU reset

commit 606af829 ("KVM: selftests: arm64: Test vCPU-scoped feature ID
registers") intended to test that MPIDR_EL1 is unchanged across vCPU
reset but failed at actually doing so.

Add the missing assertion.

Link: https://lore.kernel.org/r/20240621225045.2472090-1-oliver.upton@linux.devSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

tools/testing/selftests/kvm/aarch64/set_id_regs.c

@@ -539,6 +539,7 @@ static void test_reset_preserves_id_regs(struct kvm_vcpu *vcpu)
 	for (int i = 0; i < ARRAY_SIZE(test_regs); i++)
 		test_assert_id_reg_unchanged(vcpu, test_regs[i].reg);
 
+	test_assert_id_reg_unchanged(vcpu, SYS_MPIDR_EL1);
 	test_assert_id_reg_unchanged(vcpu, SYS_CLIDR_EL1);
 	test_assert_id_reg_unchanged(vcpu, SYS_CTR_EL0);