Fix misannotated out-of-line _copy_to_user()

Destination is a kernel pointer and source - a userland one
in _copy_from_user(); _copy_to_user() is the other way round.

Fixes: d597580d ("generic ...copy_..._user primitives")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>