Because <linux/linkage.h> doesn't exist in userspace, it should be only
included from within #ifdef __KERNEL__.  Move the corresponding #include

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>