BugLink: http://bugs.launchpad.net/bugs/1531539

There is no need to check whether dev's pages per block is
beyond rrpc support every time we init a lun, we only need
to check it once before enter the lun init loop.
Signed-off-by: Wenwei Tao <ww.tao0320@gmail.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit 4b79beb4)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>