KVM: VMX: Use kvm_read_cr4() to get cr4 value

Directly use vcpu->arch.cr4 is not recommended since it gets stale value
if the cr4 is not available.

Use kvm_read_cr4() instead to ensure correct value.
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20230410125017.1305238-2-xiaoyao.li@intel.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/vmx/vmx.c

@@ -3387,7 +3387,7 @@ static bool vmx_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 
 void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 {
-	unsigned long old_cr4 = vcpu->arch.cr4;
+	unsigned long old_cr4 = kvm_read_cr4(vcpu);
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	/*
 	 * Pass through host's Machine Check Enable value to hw_cr4, which