KVM: x86/mmu: Pass const memslot to rmap_add()

Constify rmap_add()'s @slot parameter; it is simply passed on to
gfn_to_rmap(), which takes a const memslot.

No functional change intended.
Reviewed-by: Ben Gardon <bgardon@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220516232138.1783324-15-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -1556,7 +1556,7 @@ static bool kvm_test_age_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
 
 #define RMAP_RECYCLE_THRESHOLD 1000
 
-static void rmap_add(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
+static void rmap_add(struct kvm_vcpu *vcpu, const struct kvm_memory_slot *slot,
 		     u64 *spte, gfn_t gfn)
 {
 	struct kvm_mmu_page *sp;