crypto: msm: reset pointer before returning from the function

Reset cipher_req.creq.dst and cipher_req.creq.src pointer to NULL
before returning from the function, and initialize scatterlist
variable before using it.

Change-Id: I5d5eee06a5213a05b20bf459ef0bf0c433fadbdd
Signed-off-by: Zhen Kong <zkong@codeaurora.org>