KVM: Drop unused kvm_dirty_gfn_invalid()

Drop the unused function as reported by test bot.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210901230904.15164-1-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
index 7aafefc..88f4683 100644
--- a/virt/kvm/dirty_ring.c
+++ b/virt/kvm/dirty_ring.c
@@ -91,11 +91,6 @@
 	gfn->flags = KVM_DIRTY_GFN_F_DIRTY;
 }
 
-static inline bool kvm_dirty_gfn_invalid(struct kvm_dirty_gfn *gfn)
-{
-	return gfn->flags == 0;
-}
-
 static inline bool kvm_dirty_gfn_harvested(struct kvm_dirty_gfn *gfn)
 {
 	return gfn->flags & KVM_DIRTY_GFN_F_RESET;