tty: smux_ctl: Support removing line discipline gracefully

SMUX_CTL module currently does not handle removal of the driver
gracefully. If there are any pending blocked calls on wait_event,
and the line discipline is removed, this results in accessing
destroyed wake queues.

Add support for aborting wait in response to device removal.

Change-Id: I3213306f6ed401f3abe5770ce324d9329e4dbc3f
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>