x86/mm: Remove unused variable 'old_pte'

The commit 3a19109e ("x86/mm: Fix try_preserve_large_page() to
handle large PAT bit") fixed try_preserve_large_page() by using the
corresponding pud/pmd prot/pfn interfaces, but left a variable unused
because it no longer used pte_pfn().

Later, the commit 8679de09 ("x86/mm/cpa: Split, rename and clean up
try_preserve_large_page()") renamed try_preserve_large_page() to
__should_split_large_page(), but the unused variable remains.

arch/x86/mm/pageattr.c: In function '__should_split_large_page':
arch/x86/mm/pageattr.c:741:17: warning: variable 'old_pte' set but not
used [-Wunused-but-set-variable]

Fixes: 3a19109e ("x86/mm: Fix try_preserve_large_page() to handle large PAT bit")
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: dave.hansen@linux.intel.com
Cc: luto@kernel.org
Cc: peterz@infradead.org
Cc: toshi.kani@hpe.com
Cc: bp@alien8.de
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/20190301152924.94762-1-cai@lca.pw

arch/x86/mm/pageattr.c

@@ -738,7 +738,7 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
 {
 	unsigned long numpages, pmask, psize, lpaddr, pfn, old_pfn;
 	pgprot_t old_prot, new_prot, req_prot, chk_prot;
-	pte_t new_pte, old_pte, *tmp;
+	pte_t new_pte, *tmp;
 	enum pg_level level;
 
 	/*
@@ -781,7 +781,7 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
 	 * Convert protection attributes to 4k-format, as cpa->mask* are set
 	 * up accordingly.
 	 */
-	old_pte = *kpte;
+
 	/* Clear PSE (aka _PAGE_PAT) and move PAT bit to correct position */
 	req_prot = pgprot_large_2_4k(old_prot);