Adds __init annotation at mmu_init_secondary func

[Michael Ellerman]

On Thu, 2018-07-26 at 12:52:50 UTC, Alexey Spirkov wrote:
> mmu_init_secondary function called at initialization sequence
> but it misses __init annotation. As result modpost warning is generated.
> Some building systems sensitive to such kind of warnings.
> 
> Signed-off-by: Alexey Spirkov <alexeis at astrosoft.ru>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/f7e2a152231f4a0308cc8f9c2296ba

cheers