crypto: msm: Fix failure in XTS operation

When using PIPE keys, the XTS_DU_SIZE register is hardcoded to
512 Bytes.  For transfers that are smaller than 512 bytes,
the crypto operation hangs waiting for more data.

The fix is to set XTS_DU_SIZE to minimum of packet size and 512
bytes.

Change-Id: I0dea9fadc71c599df700c1431f793e7cbb9997b0
Signed-off-by: Mona Hossain <mhossain@codeaurora.org>