asoc: msm-pcm-q6-v2: Update memset for period size

tinycap test can attempt with different size to
read from driver and need to avoid access more
than period size.

Change-Id: Ifa4ddfb086bd83aa981da62e88da3a9395f5aabc
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>