diag: Protect SMD channel from getting NULL value

DIAG driver uses SMD channel to talk to other processors.
Due to certain race condition, the SMD channel variable can
be assigned NULL value. This change prevents the NULL assignment.

Change-Id: I1a5563c51020e4107eb78429c51094d8e9f1a7ff
Signed-off-by: Shalabh Jain <shalabhj@codeaurora.org>
1 file changed