KVM: X86: Fix MSR range of APIC registers in X2APIC mode

Only MSR address range 0x800 through 0x8ff is architecturally reserved
and dedicated for accessing APIC registers in x2APIC mode.

Fixes: 0105d1a5 ("KVM: x2apic interface to lapic")
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20200616073307.16440-1-xiaoyao.li@intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>