openrisc: drop wrongly typed definition of page_to_virt()

To align with generic code and other architectures that expect the macro
page_to_virt to produce an expression whose type is 'void*', drop the
arch specific definition, which is never referenced anyway.

Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>