msm: camera: Fix possible kernel panic in general buf manager

Make sure vb2_buf is in the stream queue list to avoid potential
kernel panic if the content in the address of vb2_buf is invalid.

Change-Id: I43d66e33d0544b832b31378c01af182cfe0e8d49
Signed-off-by: Yiduo Wang <yiduow@codeaurora.org>