MIPS: Make phys_to_virt utilize __va()

The implementation is exactly the same, so avoid open-coding it in two
different locations.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/io.h

@@ -131,7 +131,7 @@ static inline phys_addr_t virt_to_phys(const volatile void *x)
  */
 static inline void * phys_to_virt(unsigned long address)
 {
-	return (void *)(address + PAGE_OFFSET - PHYS_OFFSET);
+	return __va(address);
 }
 
 /*