tty: Fix race between tty release and echo_delayed_work

Fix potential race between tty release and echo_delayed_work,
which could result in use after free scenario for tty struct.

Change-Id: I1ea0f2a17d1131c686b3fe387a3576f3d037a3a5
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>