KVM: x86/mmu: Drop new_spte local variable from restore_acc_track_spte()

The new_spte local variable is unnecessary. Deleting it can save a line
of code and simplify the remaining lines a bit.

No functional change intended.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220119230739.2234394-10-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>