msm: crypto: fix issues on digest buf and copy_from_user in qcedev.c

Make the digest length not larger than the size of the buffer
qcedev_areq.sha_op_req.digest; and use the checked variants of
the copy_from/to_user() APIs to avoid small race window of their
unchecked variants.

Change-Id: I3db0c20ac5fa47ed278f3d60368c406f472430c1
Signed-off-by: Zhen Kong <zkong@codeaurora.org>