LU-16982 ldiskfs: Fix crash after "umount -d -f /mnt/..."

LU-16982 ldiskfs: Fix crash after "umount -d -f /mnt/..."

This patch adds an extra state check during the unmount process;
Since there was the following problem:
Lustre: DEBUG MARKER: umount -d -f /mnt/lustre-mds4
kernel BUG at fs/jbd2/transaction.c:378!
CPU: 0 PID: 310834 Comm: kworker/0:2 4.18.0-477.15...
Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
Workqueue: events flush_stashed_stats_work [ldiskfs]
RIP: 0010:start_this_handle+0x22c/0x520 [jbd2]
Call Trace:
 jbd2__journal_start+0xee/0x1f0 [jbd2]
 jbd2_journal_start+0x19/0x20 [jbd2]
 flush_stashed_stats_work+0x36/0x90 [ldiskfs]
 process_one_work+0x1a7/0x360
 worker_thread+0x30/0x390
 kthread+0x134/0x150

Fixes: e27a7b33d6 ("LU-16298 ldiskfs: Periodically write ldiskfs superblock")
Signed-off-by: Vitaliy Kuznetsov <vkuznetsov@ddn.com>
Change-Id: I162d3416ca1fe9bd09f1102ccca892db05719016
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51760
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>