/proc/kpageflags: prevent an integer overflow in stable_page_flags()

/proc/kpageflags: prevent an integer overflow in stable_page_flags()

stable_page_flags() returns kpageflags info in u64, but it uses "1 <<
KPF_*" internally which is considered as int.  This type mismatch causes
no visible problem now, but it will if you set bit 32 or more as done in a
subsequent patch.  So use BIT_ULL in order to avoid future overflow
issues.

Link: http://lkml.kernel.org/r/20190725023100.31141-2-t-fukasawa@vx.jp.nec.com
Signed-off-by: Toshiki Fukasawa <t-fukasawa@vx.jp.nec.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Junichi Nomura <j-nomura@ce.jp.nec.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>