KVM: VMX: Use the correct field var when clearing VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL

Fix a recently introduced bug that results in the wrong VMCS control
field being updated when applying a IA32_PERF_GLOBAL_CTRL errata.

Fixes: c73da3fc

 ("KVM: VMX: Properly handle dynamic VM Entry/Exit controls")
Reported-by: Harald Arnesen <harald@skogtun.org>
Tested-by: Harald Arnesen <harald@skogtun.org>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>