msm: vidc: Add NULL pointer check before deiniting controls

Add NULL pointer check in deinit function, and return -EINVAL
when NULL pointer is found.
Without this change, accidentally, msm_venc_ctrl_deinit() will be called
with a null pointer parameter, which will cause kernel panic.

Change-Id: I80bb6c271dcd3277ddce5332c5f42328ca376128
CRs-Fixed: 652365
Signed-off-by: huiy <huiyQuic@codeaurora.org>