staging: lustre: fid: fix up debugfs access to ->lcs_space

staging: lustre: fid: fix up debugfs access to ->lcs_space

lcs_space can change while the lock is not held
if an RPC in underway.  This can be detected by
seq->ls_update being set.

In this case, reading or writing the value should return
-EBUSY.

Also, the D_INFO CDEBUG() which reports the lcs_space being
updated never fires, as it tests the wrong value -
ldebugfs_fid_write_common() returns 'count' on success.

Finally, this return value should be returned from
ldebugfs_fid_space_seq_write(), rather than always returning 'count',
so that errors can be detected.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>