Stop bailing out on JPEG header parsing errors during streamon.
This allows userspace to provide valid output buffers later and
fixes a v4l2-compliance streaming test failure:

		fail: v4l2-test-buffers.cpp(1429): node->streamon(q.g_type())
	test MMAP (no poll): FAIL
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>