MIPS: mm: Add prototype for function __update_cache

This commit adds a prototype to fix error at W=1:

arch/mips/mm/cache.c:129:6: error: no previous prototype
for '__update_cache' [-Werror=missing-prototypes]
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/pgtable.h

@@ -64,6 +64,7 @@ struct vm_area_struct;
 #define __S111 __pgprot(0)
 
 extern unsigned long _page_cachable_default;
+extern void __update_cache(unsigned long address, pte_t pte);
 
 /*
  * ZERO_PAGE is a global shared page that is always zero; used
@@ -224,7 +225,6 @@ static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *pt
 static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 			      pte_t *ptep, pte_t pteval)
 {
-	extern void __update_cache(unsigned long address, pte_t pte);
 
 	if (!pte_present(pteval))
 		goto cache_sync_done;

arch/mips/mm/cache.c

@@ -21,6 +21,7 @@
 #include <asm/cpu.h>
 #include <asm/cpu-features.h>
 #include <asm/setup.h>
+#include <asm/pgtable.h>
 
 /* Cache operations. */
 void (*flush_cache_all)(void);