MIPS: Fix a warning for virt_to_page

Compiling mm/highmem.c gives a warning: passing argument 1 of
'virt_to_phys' makes pointer from integer without a cast

Fixed by casting to void*

Signed-off-by: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7337/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>