msm: camera: validate num_streams in stream_cfg_cmd before using it

stream_cfg_cmd->num_streams is from userspace,
need to check it against MSM_ISP_STATS_MAX before using it.

CRs-Fixed: 2029867
Change-Id: I2ab892b7d406fc56de94c261a396866269e91d1a
Signed-off-by: Gaoxiang Chen <gaochen@codeaurora.org>
Signed-off-by: VijayaKumar T M <vtmuni@codeaurora.org>