crypto: msm: Fix buffer overflow issue

In multi-threaded environment diglen variable could be modified
by multiple threads at the same time. Buffer overflow might
happen in current thread if another thread changes the diglen
variable. So add mutex locks to avoid this issue.

Change-Id: I62c63c55c028dedb1dd0eec862851bd8e818a5d3
Signed-off-by: AnilKumar Chimata <anilc@codeaurora.org>