btrfs: sysfs, use btrfs_sysfs_remove_fsid to celanup errors in add_fsid

We have one simple function btrfs_sysfs_remove_fsid() to undo
btrfs_sysfs_add_fsid(), which also does proper checks before releasing
objects.

One difference, if btrfs_sysfs_remove_fsid is used that now we also call
kobject_del() which was missing before. This was tested (with kobject
debug turned on) and no change in behaviour was found.

This is a cleanup patch.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>