msm: vidc: modify v4l2 mbaff flag to avoid conflict

Currently V4L2_MSM_BUF_FLAG_MBAFF is defined using the same
value as V4L2_BUF_FLAG_LAST, this will cause H264 MBAFF clips
can't playback successfully.
Modify to use another bit for V4L2_MSM_BUF_FLAG_MBAFF.

CRs-Fixed: 2213243
Change-Id: I31cbc79dad55f391d7a0509f9e918b94d22f32ea
Signed-off-by: Qiwei Liu <qiweil@codeaurora.org>