dsp: avtimer: add __user attribute to identify userspace address

Add __user attribute for avtimer_ioctl's input parameter ioctl_param
to explicitly identify user space pointer in copy_to_user.

Change-Id: I59fa9d39e5ec3ff9cde3a06af9da2d38e36d557d
Signed-off-by: Xiaoyu Ye <benyxy@codeaurora.org>