[PATCH] Add const to pointer qualifiers for __chk_user_ptr and __chk_io_ptr.

Change prototypes for __chk_user_ptr and __chk_io_ptr to take const
void* instead of void*, so that code can pass "const void *" to them.

(Right now sparse does not warn about passing const void* to void*
functions, but that is a separate bug that I believe Josh is working on,
and once sparse does check this, the changed prototypes will be
necessary.)

Signed-off-by: Russ Cox <rsc@swtch.com>
Signed-off-by: Josh Triplett <josh@freedesktop.org>
Acked-by: Christopher Li <sparse@chrisli.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>