[PORT FROM R2]HSU Driver: fix possible memory leak

[PORT FROM R2]HSU Driver: fix possible memory leak

BZ: 26435

In hsu_startup function, DMA buffer was allocated. while in
hsu_shutdown function, the allocated buffer is not free. So
potentially this will cause memory leak.

Change-Id: I706eab1dafcc728a77f38fca8b3253e6b46bd37f
Orig-Change-Id: I85a03246fcaa6a85b8ba8d254b8b4684036355f6
Signed-off-by: Even Xu <feng.xu@intel.com>
Reviewed-on: http://android.intel.com:8080/38074
Reviewed-by: Du, Alek <alek.du@intel.com>
Tested-by: Wang, Zhifeng <zhifeng.wang@intel.com>
Reviewed-by: Kuppuswamy, Sathyanarayanan <sathyanarayanan.kuppuswamy@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>