KVM: x86/mmu: rephrase unclear comment

If accessed bits are not supported there simple isn't any distinction
between accessed and non-accessed gPTEs, so the comment does not make
much sense.  Rephrase it in terms of what happens if accessed bits
*are* supported.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/paging_tmpl.h

@@ -151,7 +151,7 @@ static bool FNAME(prefetch_invalid_gpte)(struct kvm_vcpu *vcpu,
 	if (!FNAME(is_present_gpte)(gpte))
 		goto no_present;
 
-	/* if accessed bit is not supported prefetch non accessed gpte */
+	/* Prefetch only accessed entries (unless A/D bits are disabled). */
 	if (PT_HAVE_ACCESSED_DIRTY(vcpu->arch.mmu) &&
 	    !(gpte & PT_GUEST_ACCESSED_MASK))
 		goto no_present;