autodisc: cast when assigning to different enum type

autodisc: cast when assigning to different enum type

Gets rid of these warnings with clang:

    /home/smarchi/src/babeltrace/src/autodisc/autodisc.c:766:13: warning: implicit conversion from enumeration type 'auto_source_discovery_internal_status' (aka 'enum auto_source_discovery_internal_status') to different enumeration type 'auto_source_discovery_status' (aka 'enum auto_source_discovery_status') [-Wenum-conversion]
                            status = internal_status;
                                   ~ ^~~~~~~~~~~~~~~
    /home/smarchi/src/babeltrace/src/autodisc/autodisc.c:778:13: warning: implicit conversion from enumeration type 'auto_source_discovery_internal_status' (aka 'enum auto_source_discovery_internal_status') to different enumeration type 'auto_source_discovery_status' (aka 'enum auto_source_discovery_status') [-Wenum-conversion]
                            status = internal_status;
                                   ~ ^~~~~~~~~~~~~~~

Change-Id: Id4cdaaf20da1789e604d346ff2c08239352eb381
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1975
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>