MIPS: KVM: Fix a build warning about variable set but not used

After commit 411740f ("KVM: MIPS/MMU: Implement KVM_CAP_SYNC_MMU")
old_pte is no longer used in kvm_mips_map_page(). So remove it to fix a
build warning about variable set but not used:

   arch/mips/kvm/mmu.c: In function 'kvm_mips_map_page':
>> arch/mips/kvm/mmu.c:701:29: warning: variable 'old_pte' set but not used [-Wunused-but-set-variable]
     701 |         pte_t *ptep, entry, old_pte;
         |                             ^~~~~~~

Cc: [email protected]
Fixes: 411740f ("KVM: MIPS/MMU: Implement KVM_CAP_SYNC_MMU")
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Huacai Chen <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Thomas Bogendoerfer <[email protected]>

Author: chenhuacai

arch/mips/kvm/mmu.c

@@ -592,7 +592,7 @@ static int kvm_mips_map_page(struct kvm_vcpu *vcpu, unsigned long gpa,
 	gfn_t gfn = gpa >> PAGE_SHIFT;
 	int srcu_idx, err;
 	kvm_pfn_t pfn;
-	pte_t *ptep, entry, old_pte;
+	pte_t *ptep, entry;
 	bool writeable;
 	unsigned long prot_bits;
 	unsigned long mmu_seq;
@@ -664,7 +664,6 @@ static int kvm_mips_map_page(struct kvm_vcpu *vcpu, unsigned long gpa,
 	entry = pfn_pte(pfn, __pgprot(prot_bits));
 
 	/* Write the PTE */
-	old_pte = *ptep;
 	set_pte(ptep, entry);
 
 	err = 0;