KVM: x86: Fix constant value of VM_{EXIT_SAVE,ENTRY_LOAD}_DEBUG_CONTROLS

The spec says those controls are at bit position 2 - makes 4 as value.

The impact of this mistake is effectively zero as we only use them to
ensure that these features are set at position 2 (or, previously, 1) in
MSR_IA32_VMX_{EXIT,ENTRY}_CTLS - which is and will be always true
according to the spec.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>