[MIPS] unexport copy_user_highpage()

The copy_user_highpage() routine has no users outside of the
core kernel code, so exporting this symbol is pointless.
This patch removes EXPORT_SYMBOL(copy_user_highpage).

Signed-off-by: Dmitri Vorobiev <dmitri.vorobiev@gmail.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/init.c

@@ -229,8 +229,6 @@ void copy_user_highpage(struct page *to, struct page *from,
 	smp_wmb();
 }
 
-EXPORT_SYMBOL(copy_user_highpage);
-
 void copy_to_user_page(struct vm_area_struct *vma,
 	struct page *page, unsigned long vaddr, void *dst, const void *src,
 	unsigned long len)