msm: vidc: Correct calculation of yuv buffer size

Improper yuv buffer size is being calculated using frame
height directly, which is resulting into failures during
encoding if the frame height is not aligned to 16.
With this change, yuv buffer size calculation is done
properly by using scanlines in place of frame height.

Change-Id: I22602d6a0eddfa4016f4bdc3479e5b7d9b89a4e7
CRs-Fixed: 378988
Signed-off-by: Deepak Verma <dverma@codeaurora.org>