KVM: TDX: Remove __user annotation from kernel pointer

Separate __user pointer variable declaration from kernel one.

There are two 'kvm_cpuid2' pointers involved here. There's an "input"
side: 'td_cpuid' which is a normal kernel pointer and an 'output'
side. The output here is userspace and there is an attempt at properly
annotating the variable with __user:

	struct kvm_cpuid2 __user *output, *td_cpuid;

But, alas, this is wrong. The __user in the definition applies to both
'output' and 'td_cpuid'. Sparse notices the address space mismatch and
will complain about it.

Fix it up by completely separating the two definitions so that it is
obviously correct without even having to know what the C syntax rules
even are.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Fixes: 488808e682 ("KVM: x86: Introduce KVM_TDX_GET_CPUID")
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/20251103234437.A0532420@davehans-spike.ostc.intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/vmx/tdx.c

@@ -3038,7 +3038,8 @@ static int tdx_vcpu_get_cpuid_leaf(struct kvm_vcpu *vcpu, u32 leaf, int *entry_i
 
 static int tdx_vcpu_get_cpuid(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *cmd)
 {
-	struct kvm_cpuid2 __user *output, *td_cpuid;
+	struct kvm_cpuid2 __user *output;
+	struct kvm_cpuid2 *td_cpuid;
 	int r = 0, i = 0, leaf;
 	u32 level;