init: mark __user address space on string literals

When calling syscall service routines in kernel, some of arguments should
be user pointers but were missing __user markup on string literals.  Add
it.  Removes some sparse warnings.

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Phillip Lougher <phillip@lougher.demon.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>