KVM: selftests: fix rdtsc() for vmx_tsc_adjust_test

KVM: selftests: fix rdtsc() for vmx_tsc_adjust_test

vmx_tsc_adjust_test fails with:

IA32_TSC_ADJUST is -4294969448 (-1 * TSC_ADJUST_VALUE + -2152).
IA32_TSC_ADJUST is -4294969448 (-1 * TSC_ADJUST_VALUE + -2152).
IA32_TSC_ADJUST is 281470681738540 (65534 * TSC_ADJUST_VALUE + 4294962476).
==== Test Assertion Failure ====
  x86_64/vmx_tsc_adjust_test.c:153: false
  pid=19738 tid=19738 - Interrupted system call
     1	0x0000000000401192: main at vmx_tsc_adjust_test.c:153
     2	0x00007fe1ef8583d4: ?? ??:0
     3	0x0000000000401201: _start at ??:?
  Failed guest assert: (adjust <= max)

The problem is that is 'tsc_val' should be u64, not u32 or the reading
gets truncated.

Fixes: 8d7fbf01f9afc ("KVM: selftests: VMX preemption timer migration test")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200601154726.261868-1-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>