TTY: msm_smd_tty: Fix clean up tty devices in fail case

Smd tty device index read by old device tree label causing the
clean-up code to exit abruptly and resulting in a crash during
re-registration with fall back option.

Read the smd tty device index with proper label and do the clean-up
complete.

CRs-Fixed: 669452
Change-Id: Ib317a035e51ca8040b199bc1a9986b731e59410d
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>