KVM: MMU: remove rmap before clear spte

Remove rmap before clear spte otherwise it will trigger BUG_ON() in
some functions such as rmap_write_protect().

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/mmu.c

@@ -1813,6 +1813,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 		if (level > PT_PAGE_TABLE_LEVEL &&
 		    has_wrprotected_page(vcpu->kvm, gfn, level)) {
 			ret = 1;
+			rmap_remove(vcpu->kvm, sptep);
 			spte = shadow_trap_nonpresent_pte;
 			goto set_pte;
 		}