[MIPS] Fix CONFIG_LIMITED_DMA build.

This fix a build error for the Momentum Jaguar ATX eval board.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/mm/highmem.c b/arch/mips/mm/highmem.c
index 1f7b37b..0c54437 100644
--- a/arch/mips/mm/highmem.c
+++ b/arch/mips/mm/highmem.c
@@ -83,6 +83,7 @@
 	preempt_check_resched();
 }
 
+#ifndef CONFIG_LIMITED_DMA
 /*
  * This is the same as kmap_atomic() but can map memory that doesn't
  * have a struct page associated with it.
@@ -101,6 +102,7 @@
 
 	return (void*) vaddr;
 }
+#endif /* CONFIG_LIMITED_DMA */
 
 struct page *__kmap_atomic_to_page(void *ptr)
 {