bcachefs: respect superblock discard flag.

We were accidentally using default mount options and overwriting the
discard flag.
Signed-off-by: Daniel Hill <daniel@gluo.nz>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/super.c

@@ -1167,9 +1167,6 @@ static struct bch_dev *__bch2_dev_alloc(struct bch_fs *c,
 	ca->mi = bch2_mi_to_cpu(member);
 	ca->uuid = member->uuid;
 
-	if (opt_defined(c->opts, discard))
-		ca->mi.discard = opt_get(c->opts, discard);
-
 	if (percpu_ref_init(&ca->ref, bch2_dev_ref_complete,
 			    0, GFP_KERNEL) ||
 	    percpu_ref_init(&ca->io_ref, bch2_dev_io_ref_complete,