KVM: x86: Relocate MMIO exit stats counting

Move the stat.mmio_exits update into x86_emulate_instruction().  This is
both a bug fix, e.g. the current update flows will incorrectly increment
mmio_exits on emulation failure, and a preparatory change to set the
stage for eliminating EMULATE_DONE and company.
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -5456,8 +5456,6 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
 	case EMULATE_DONE:
 		return 1;
 	case EMULATE_USER_EXIT:
-		++vcpu->stat.mmio_exits;
-		/* fall through */
 	case EMULATE_FAIL:
 		return 0;
 	default:

arch/x86/kvm/vmx/vmx.c

@@ -5201,7 +5201,6 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
 		err = kvm_emulate_instruction(vcpu, 0);
 
 		if (err == EMULATE_USER_EXIT) {
-			++vcpu->stat.mmio_exits;
 			ret = 0;
 			goto out;
 		}

arch/x86/kvm/x86.c

@@ -6703,6 +6703,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 		}
 		r = EMULATE_USER_EXIT;
 	} else if (vcpu->mmio_needed) {
+		++vcpu->stat.mmio_exits;
+
 		if (!vcpu->mmio_is_write)
 			writeback = false;
 		r = EMULATE_USER_EXIT;