ASoC: msm: Fix for passing correct data to userspace

The Copy_to_user function copies the whole frame structure
to the userspace. Only len bytes should be copied.
As the whole frame is being copied
(HPCM_MAX_VOC_PKT_SIZE bytes) the uninitialized bytes
in the buffer will be disclosed to the calling
user-space process.

Change-Id: I7d7f58d358aaf56d91a79cfe95c04d937b48da53
Signed-off-by: Vicky Sehrawat <vickys@codeaurora.org>