pmu-chained-counters in ubuntu_kvm_unit_tests failed with B-4.15 ARM64

Issue found on 4.15.0-157.164 with ARM64 node appleton-kernel

Test failed with:
 FAIL: pmu: pmu-chained-counters: CHAIN counter #1 incremented
 FAIL: pmu: pmu-chained-counters: CHAIN counter #1 set to 2
 FAIL: pmu: pmu-chained-counters: CHAIN counter #1 wrapped
 FAIL: pmu: pmu-chained-counters: overflow on chain counter

Test log:
Running '/home/ubuntu/autotest/client/tmp/ubuntu_kvm_unit_tests/src/kvm-unit-tests/tests/pmu-chained-counters'
 BUILD_HEAD=1593e88a
 timeout -k 1s --foreground 90s /usr/bin/qemu-system-aarch64 -nodefaults -machine virt,gic-version=host,accel=kvm -cpu host -device virtio-serial-device -device virtconsole,chardev=ctd -chardev testdev,id=ctd -device pci-testdev -display none -serial stdio -kernel /tmp/tmp.bQd7EQAmtH -smp 1 -append pmu-chained-counters # -initrd /tmp/tmp.89PxrSoymL
 INFO: PMU version: 0x1
 INFO: PMU implementer/ID code: 0x41("A")/0x2
 INFO: Implements 6 event counters
 FAIL: pmu: pmu-chained-counters: CHAIN counter #1 incremented
 PASS: pmu: pmu-chained-counters: no overflow recorded for chained incr #1
 INFO: pmu: pmu-chained-counters: overflow reg = 0x0
 FAIL: pmu: pmu-chained-counters: CHAIN counter #1 set to 2
 PASS: pmu: pmu-chained-counters: no overflow recorded for chained incr #2
 INFO: pmu: pmu-chained-counters: overflow reg = 0x0
 FAIL: pmu: pmu-chained-counters: CHAIN counter #1 wrapped
 FAIL: pmu: pmu-chained-counters: overflow on chain counter
 SUMMARY: 6 tests, 4 unexpected failures
 FAIL pmu-chained-counters (6 tests, 4 unexpected failures)

This issue can be found with 4.15.0-154.161 as well. Not a regression.