mips: provide unxlate_dev_mem_ptr() in asm/io.h

The unxlate_dev_mem_ptr() function has no prototype on the mips
architecture, which does not include asm-generic/io.h, so gcc warns
about the __weak definition:

drivers/char/mem.c:94:29: error: no previous prototype for 'unxlate_dev_mem_ptr' [-Werror=missing-prototypes]

Since everyone else already gets the generic definition or has a custom
one, there is not really much point in having a __weak version as well.

Remove this one, and instead add a trivial macro to the mips header.
Once we convert mips to use the asm-generic header, this can go away
again.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/io.h

@@ -554,6 +554,7 @@ extern void (*_dma_cache_inv)(unsigned long start, unsigned long size);
  * access
  */
 #define xlate_dev_mem_ptr(p)	__va(p)
+#define unxlate_dev_mem_ptr(p, v) do { } while (0)
 
 void __ioread64_copy(void *to, const void __iomem *from, size_t count);
 

drivers/char/mem.c

@@ -90,13 +90,6 @@ static inline int range_is_allowed(unsigned long pfn, unsigned long size)
 }
 #endif
 
-#ifndef unxlate_dev_mem_ptr
-#define unxlate_dev_mem_ptr unxlate_dev_mem_ptr
-void __weak unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
-{
-}
-#endif
-
 static inline bool should_stop_iteration(void)
 {
 	if (need_resched())