KVM: TDX: Fix sparse warnings from using 0 for NULL

Stop using 0 for NULL.

sparse moans:

	... arch/x86/kvm/vmx/tdx.c:859:38: warning: Using plain integer as NULL pointer

for several TDX pointer initializations. While I love a good ptr=0
now and then, it's good to have quiet sparse builds.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Fixes: a50f673 ("KVM: TDX: Do TDX specific vcpu initialization")
Fixes: 8d032b6 ("KVM: TDX: create/destroy VM structure")
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Xiaoyao Li <xiaoyao.li@intel.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Kirill A. Shutemov" <kas@kernel.org>
Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Acked-by: Kiryl Shutsemau <kas@kernel.org>
Link: https://patch.msgid.link/20251103234439.DC8227E4@davehans-spike.ostc.intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: hansendc

arch/x86/kvm/vmx/tdx.c

@@ -903,7 +903,7 @@ void tdx_vcpu_free(struct kvm_vcpu *vcpu)
 	}
 	if (tdx->vp.tdvpr_page) {
 		tdx_reclaim_control_page(tdx->vp.tdvpr_page);
-		tdx->vp.tdvpr_page = 0;
+		tdx->vp.tdvpr_page = NULL;
 		tdx->vp.tdvpr_pa = 0;
 	}
 
@@ -2581,7 +2581,7 @@ static int __tdx_td_init(struct kvm *kvm, struct td_params *td_params,
 free_tdr:
 	if (tdr_page)
 		__free_page(tdr_page);
-	kvm_tdx->td.tdr_page = 0;
+	kvm_tdx->td.tdr_page = NULL;
 
 free_hkid:
 	tdx_hkid_free(kvm_tdx);
@@ -3000,7 +3000,7 @@ static int tdx_td_vcpu_init(struct kvm_vcpu *vcpu, u64 vcpu_rcx)
 free_tdvpr:
 	if (tdx->vp.tdvpr_page)
 		__free_page(tdx->vp.tdvpr_page);
-	tdx->vp.tdvpr_page = 0;
+	tdx->vp.tdvpr_page = NULL;
 	tdx->vp.tdvpr_pa = 0;
 
 	return ret;