media: imx-jpeg: Drop initial source change event if capture has been setup

In section 4.5.1.5. Initialization, the step 4 may be skipped and
continue with the Capture Setup sequence, so if the capture has been
setup, there is no need to trigger the initial source change event, just
start decoding, and follow the dynamic resolution change flow if the
configured values do not match those parsed by the decoder.

And it won't fail the gstreamer pipeline.

Fixes: b833b178 ("media: imx-jpeg: notify source chagne event when the first picture parsed")
Signed-off-by: Ming Qian <ming.qian@nxp.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>