crypto: msm: Use scnprintf() instead of snprintf()

snprintf can return more than the size of buffer, which is not
expected here, obviously. Use scnprintf instead.

Change-Id: I3b97a016df910728dfef5a0914ab8ad67c68e39c
Signed-off-by: AnilKumar Chimata <anilc@codeaurora.org>