userfaultfd: remove wrong comment from userfaultfd_ctx_get()

It's a void function, so there is no return value;

Link: http://lkml.kernel.org/r/20170309150817.7510-1-david@redhat.com


Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>