lightnvm: pblk: clear flush point on completed writes
Move completion of syncs and clearing of flush points to the
write completion path - this ensures that the data has been
comitted to the media before completing bios containing syncs.
Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com> Signed-off-by: Javier González <javier@cnexlabs.com> Signed-off-by: Matias Bjørling <m@bjorling.me> Signed-off-by: Jens Axboe <axboe@kernel.dk>