hso serial throttled tty kref fix.

This patch is for Alan Cox as it related to the tty layer.
Hopefully the hso driver is again relatively stable with this fix.

Signed-off-by: Denis Joseph Barrow <D.Barow@option.com>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>