kernel/sysctl.c: fix typos in comments

Fix a few typos/spellos in kernel/sysctl.c.

Link: http://lkml.kernel.org/r/bb09a8b9-f984-6dd4-b07b-3ecaf200862e@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>