mm/page_poison.c: make early_page_poison_param() __init

mm/page_poison.c: make early_page_poison_param() __init

The early_param() is only called during kernel initialization, So Linux
marks the function of it with __init macro to save memory.

But it forgot to mark the early_page_poison_param().  So, Make it __init
as well.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Dou Liyang <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Philippe Ombredanne <[email protected]>
Cc: Kate Stewart <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>