KVM: MMU: Report spte not found in rmap before BUG()

In the past we've had errors of single-bit in the other two cases; the
printk() may confirm it for the third case (many->many).

Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/mmu.c

@@ -662,6 +662,7 @@ static void rmap_remove(struct kvm *kvm, u64 *spte)
 			prev_desc = desc;
 			desc = desc->more;
 		}
+		pr_err("rmap_remove: %p %llx many->many\n", spte, *spte);
 		BUG();
 	}
 }