f2fs-tools: fix the wrong message when errno is EBUSY

f2fs-tools: fix the wrong message when errno is EBUSY

If f2fs is unmounted with the -l option, the process can still use the
file system. In this case, the command mkfs.f2fs, fsck.f2fs, dump.f2fs,
defrag.f2fs, resize.f2fs and sload.f2fs failed due to the device is in
use by the system. At the moment f2fs is already not mounted, so it is
wrong to print error message "Error: Not available on mounted device!",
this patch fixes it.

[root@localhost home]# mkfs.f2fs -f /dev/sdb1
[root@localhost home]# mkdir -p /mnt/f2fs_mnt_point
[root@localhost home]# mount -t f2fs /dev/sdb1 /mnt/f2fs_mnt_point/
[root@localhost home]# cd /mnt/f2fs_mnt_point/
[root@localhost f2fs_mnt_point]# umount /dev/sdb1
umount: /mnt/f2fs_mnt_point: target is busy.
        (In some cases useful info about processes that use
         the device is found by lsof(8) or fuser(1))
[root@localhost f2fs_mnt_point]# umount -l /dev/sdb1
[root@localhost f2fs_mnt_point]# umount /dev/sdb1
umount: /dev/sdb1: not mounted
[root@localhost f2fs_mnt_point]# mkfs.f2fs -f /dev/sdb1

	F2FS-tools: mkfs.f2fs Ver: 1.8.0 (2017-04-28)

Info: Disable heap-based policy
Info: Debug level = 0
Info: Label =
Info: Trim is enabled
	Error: In use by the system!
	Error: Not available on mounted device!
[root@localhost f2fs_mnt_point]# fsck.f2fs /dev/sdb1
	Error: In use by the system!
	Error: Not available on mounted device!
[root@localhost f2fs_mnt_point]# dump.f2fs /dev/sdb1
	Error: In use by the system!
	Error: Not available on mounted device!
[root@localhost f2fs_mnt_point]# defrag.f2fs /dev/sdb1
	Error: In use by the system!
	Error: Not available on mounted device!
[root@localhost f2fs_mnt_point]# resize.f2fs /dev/sdb1
	Error: In use by the system!
	Error: Not available on mounted device!
[root@localhost f2fs_mnt_point]# sload.f2fs /dev/sdb1
	Error: In use by the system!
	Error: Not available on mounted device!

Signed-off-by: Tiezhu Yang <kernelpatch@126.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>