lightnvm: pblk: set proper read status in bio

Currently in case of read errors, bi_status is not set properly which
leads to returning inproper data to layers above. This patch fix that
by setting proper status in case of read errors.

Also remove unnecessary warn_once(), which does not make sense
in that place, since user bio is not used for interation with drive
and thus bi_status will not be set here.

Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
Reviewed-by: Javier González <javier@javigon.com>
Reviewed-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>