smdk4412-common: camera: don't propogate cancel autofocus in CAF

Setting AUTO_FOCUS_OFF during CAF mode seems to be dangerous and hangs
the sensor. Hence, we only propogate V4L2_CID_CAMERA_SET_AUTO_FOCUS if
we have previously started the Autofocus (Manual/Touch).

Change-Id: Ia081257c16f2b7a2e2d6a1e93e239179f39c3fec