Revert "ARC: mm: don't loose PTE_SPECIAL in pte_modify()"

This reverts commit 77c6ffdb.
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

arch/arc/include/asm/pgtable.h

@@ -98,7 +98,7 @@
 #define ___DEF (_PAGE_PRESENT | _PAGE_DEF_CACHEABLE)
 
 /* Set of bits not changed in pte_modify */
-#define _PAGE_CHG_MASK	(PAGE_MASK | _PAGE_ACCESSED | _PAGE_MODIFIED | _PAGE_SPECIAL)
+#define _PAGE_CHG_MASK	(PAGE_MASK | _PAGE_ACCESSED | _PAGE_MODIFIED)
 
 /* More Abbrevaited helpers */
 #define PAGE_U_NONE     __pgprot(___DEF)