msm: vidc: Check for frame size for calculating CF

If height and width are small resulting into less
MBs per frame then frame size might result into
zero after division from a factor of (32*8*3)/2.
So clipping max value of CF at (4 << 16).

CRs-Fixed: 2167880
Change-Id: I640a46d1ed627a6e15523e96781d07c514ac9734
Signed-off-by: Prateek Shrivastava <pshrivas@codeaurora.org>