[MIPS] "extern inline" -> "static inline"

"extern inline" will have different semantics with gcc 4.3, and
"static inline" is correct here.
Signed-off-by: NAdrian Bunk <bunk@stusta.de>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

include/asm-mips/processor.h

@@ -237,7 +237,7 @@ unsigned long get_wchan(struct task_struct *p);
 
 #define ARCH_HAS_PREFETCH
 
-extern inline void prefetch(const void *addr)
+static inline void prefetch(const void *addr)
 {
 	__asm__ __volatile__(
 	"	.set	mips4		\n"