Add a version of cameraData() that returns a const pointer and mark it
as a const operation. The assert in the non-const version of the
function already enforces that a std::map::at() operation would always
succeed so there is no change in operation from the non-const version.
Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
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