compat: copy missing fields in compat_statfs64 to user

f_flags and f_spare fields were not copied to userspace when
compat_sys_[f]statfs64 called.

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>