TTY: msm_smd_tty: Fix simultaneous open/close race condition

smd_tty_close currently has a variable that depends on a race
condition with tty_port_open. This causes a null-pointer dereference
when the same port is simultaneously being opened/closed.

Use data from a static array instead of the variable to eliminate
the race condition.

CRs-Fixed: 624398
Change-Id: Ie55d37feaadd3a15f64e18501cd3af19145dbc8e
Signed-off-by: Steven Cahail <scahail@codeaurora.org>