msm: camera: isp: fix for enqueue buffer failure

Return values are not handled in this msm_isp_proc_buf_cmd.
Though buffer enqueue or dequeue failed, still returning 0.

CRs-Fixed: 2002948

Change-Id: I9cb8c79f0155e658d4c7918b271ec025758b575f
Signed-off-by: Senthil Kumar Rajagopal <skrajago@codeaurora.org>