source.text.dmesg: replace switch to convert status with cast

source.text.dmesg: replace switch to convert status with cast

Replace the switch currently used in create_port, to convert the status of
bt_self_component_source_add_output_port, with a simple cast, as per standard
procedure.  Since create_port becomes trivial, remove it and inline the code in dmesg_init.

Change-Id: Iccdf0ba298c73616b7c86b14e5208de4519b77d8
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/3395
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>