msm: vidc: align input buffer size to 4k for secure usecase

Set format will not update buffer size if there is no change
in format, width or height. So align input buffer size
in kernel once halved during secure playback usecases.

Change-Id: Ic7604d3f1bcefb9193c676e81691cc370018a807
Signed-off-by: Govindaraj Rajagopal <grajagop@codeaurora.org>