Inline the function as it is only used in a single place and does not do
anything complicated. This also lets the `operator==` of `std::optional`
take care of the proper comparison instead of defaulting the value to -1
and comparing that.
Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
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