KVM: x86: Dedup fastpath MSR post-handling logic

Now that the WRMSR fastpath for x2APIC_ICR and TSC_DEADLINE are identical,
ignoring the backend MSR handling, consolidate the common bits of skipping
the instruction and setting the return value.

No functional change intended.

Link: https://lore.kernel.org/r/20240802195120.325560-3-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/x86.c

@@ -2186,31 +2186,32 @@ fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu)
 {
 	u32 msr = kvm_rcx_read(vcpu);
 	u64 data;
-	fastpath_t ret = EXIT_FASTPATH_NONE;
+	fastpath_t ret;
+	bool handled;
 
 	kvm_vcpu_srcu_read_lock(vcpu);
 
 	switch (msr) {
 	case APIC_BASE_MSR + (APIC_ICR >> 4):
 		data = kvm_read_edx_eax(vcpu);
-		if (!handle_fastpath_set_x2apic_icr_irqoff(vcpu, data)) {
-			kvm_skip_emulated_instruction(vcpu);
-			ret = EXIT_FASTPATH_REENTER_GUEST;
-		}
+		handled = !handle_fastpath_set_x2apic_icr_irqoff(vcpu, data);
 		break;
 	case MSR_IA32_TSC_DEADLINE:
 		data = kvm_read_edx_eax(vcpu);
-		if (!handle_fastpath_set_tscdeadline(vcpu, data)) {
-			kvm_skip_emulated_instruction(vcpu);
-			ret = EXIT_FASTPATH_REENTER_GUEST;
-		}
+		handled = !handle_fastpath_set_tscdeadline(vcpu, data);
 		break;
 	default:
+		handled = false;
 		break;
 	}
 
-	if (ret != EXIT_FASTPATH_NONE)
+	if (handled) {
+		kvm_skip_emulated_instruction(vcpu);
+		ret = EXIT_FASTPATH_REENTER_GUEST;
 		trace_kvm_msr_write(msr, data);
+	} else {
+		ret = EXIT_FASTPATH_NONE;
+	}
 
 	kvm_vcpu_srcu_read_unlock(vcpu);