msm: camera: make sure num_buf is not out of bound

V4L2 only allow 32 buffers. Check the num_buf to make sure that
user space passed value is not out of bound.

CRs-Fixed: 514698
Change-Id: I662ec1eb998ed8bfb2a7f188e645410aa78c83b0
Signed-off-by: Hariram Purushothaman <hpurus@codeaurora.org>
Signed-off-by: Ankit Premrajka <ankitp@codeaurora.org>
Signed-off-by: Raghu DP <dp.raghu@codeaurora.org>