fs/compat_ioctl: fix build when !BLOCK

In file included from fs/compat_ioctl.c:61:
include/linux/loop.h:59: error: field 'lo_bio_list' has incomplete type

Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>