When no log category is specified, `nullptr` is passed, and
then the `_log()` function implementations replace that with
`LogCategory::defaultCategory()`. But since the call site always
knows the log category, this condition can be removed and the
`_LOG1()` macro can use `LogCategory::defaultCategory()`.
So remove the condition from the `_log()` implementations and
use references to refer to log categories.
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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