KVM: selftests: Print out the actual Top-Down Slots count on failure

Print out the expected vs. actual count of the Top-Down Slots event on
failure in the Intel PMU counters test.  GUEST_ASSERT() only expands
constants/macros, i.e. only prints the value of the expected count, which
makes it difficult to debug and triage failures.

Link: https://lore.kernel.org/r/20250117234204.2600624-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

tools/testing/selftests/kvm/x86/pmu_counters_test.c

@@ -174,7 +174,9 @@ static void guest_assert_event_count(uint8_t idx, uint32_t pmc, uint32_t pmc_msr
 		GUEST_ASSERT_NE(count, 0);
 		break;
 	case INTEL_ARCH_TOPDOWN_SLOTS_INDEX:
-		GUEST_ASSERT(count >= NUM_INSNS_RETIRED);
+		__GUEST_ASSERT(count >= NUM_INSNS_RETIRED,
+			       "Expected top-down slots >= %u, got count = %lu",
+			       NUM_INSNS_RETIRED, count);
 		break;
 	default:
 		break;