loop: Fix occasional uevent drop

Commit 716ad098 ("loop: Switch to set_capacity_revalidate_and_notify")
causes an occasional drop of loop device uevent, which are no longer
triggered in loop_set_size() but in a different part of code.

Bug is reproducible with LTP test uevent01 [1]:

i=0; while true; do
    i=$((i+1)); echo "== $i =="
    lsmod |grep -q loop && rmmod -f loop
    ./uevent01 || break
done

Put back triggering through code called in loop_set_size().

Fix required to add yet another parameter to
set_capacity_revalidate_and_notify().

[1] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/uevents/uevent01.c

[hch: rebased on a different change to the prototype of
 set_capacity_revalidate_and_notify]

Cc: stable@vger.kernel.org # v5.9
Fixes: 716ad098 ("loop: Switch to set_capacity_revalidate_and_notify")
Reported-by: <ltp@lists.linux.it>
Signed-off-by: NPetr Vorel <pvorel@suse.cz>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/block/loop.c

@@ -255,7 +255,8 @@ static void loop_set_size(struct loop_device *lo, loff_t size)
 
 	bd_set_nr_sectors(bdev, size);
 
-	set_capacity_revalidate_and_notify(lo->lo_disk, size, false);
+	if (!set_capacity_revalidate_and_notify(lo->lo_disk, size, false))
+		kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
 }
 
 static inline int