loop: Fix missing discard support when using LOOP_CONFIGURE

Without calling loop_config_discard() the discard flag and parameters
aren't set/updated for the loop device and worst-case they could
indicate discard support when it isn't the case (ex: if the
LOOP_SET_STATUS ioctl was used with a different file prior to
LOOP_CONFIGURE).

Cc: <stable@vger.kernel.org> # 5.8.x-
Fixes: 3448914e8cc5 ("loop: Add LOOP_CONFIGURE ioctl")
Signed-off-by: Kristian Klausen <kristian@klausen.dk>
Link: https://lore.kernel.org/r/20210618115157.31452-1-kristian@klausen.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index d58d68f..fda071f 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1154,6 +1154,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
 	blk_queue_physical_block_size(lo->lo_queue, bsize);
 	blk_queue_io_min(lo->lo_queue, bsize);
 
+	loop_config_discard(lo);
 	loop_update_rotational(lo);
 	loop_update_dio(lo);
 	loop_sysfs_init(lo);