media: ipu6: Remove source_entity from struct ipu6_isys_stream

media: ipu6: Remove source_entity from struct ipu6_isys_stream

Remove source_entity from struct ipu6_isys_stream and instead pass it on
in function arguments.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Bingbu Cao <bingbu.cao@intel.com>
Tested-by: Mehdi Djait <mehdi.djait@linux.intel.com> # Dell XPS 9315
Reviewed-by: Mehdi Djait <mehdi.djait@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>