powerpc/mm: Fix compiler warning in pgtable-ppc64.h [-Wunused-but-set-variable]

The variable 'old' is set but not used in the wrprotect functions in
arch/powerpc/include/asm/pgtable-ppc64.h, which can trigger a compiler warning.

Remove the variable, since it's not used anyway.
Signed-off-by: Stratos Psomadakis <psomas@ece.ntua.gr>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/pgtable-ppc64.h

@@ -257,21 +257,20 @@ static inline int __ptep_test_and_clear_young(struct mm_struct *mm,
 static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr,
 				      pte_t *ptep)
 {
-	unsigned long old;
 
-       	if ((pte_val(*ptep) & _PAGE_RW) == 0)
-       		return;
-	old = pte_update(mm, addr, ptep, _PAGE_RW, 0);
+	if ((pte_val(*ptep) & _PAGE_RW) == 0)
+		return;
+
+	pte_update(mm, addr, ptep, _PAGE_RW, 0);
 }
 
 static inline void huge_ptep_set_wrprotect(struct mm_struct *mm,
 					   unsigned long addr, pte_t *ptep)
 {
-	unsigned long old;
-
 	if ((pte_val(*ptep) & _PAGE_RW) == 0)
 		return;
-	old = pte_update(mm, addr, ptep, _PAGE_RW, 1);
+
+	pte_update(mm, addr, ptep, _PAGE_RW, 1);
 }
 
 /*