Fix: src.text.dmesg: add missing assignment of `status` on error path

Fix: src.text.dmesg: add missing assignment of `status` on error path

The error path under `if (!*msg)`, originally at line 789, is missing
assigning an error status to the `status` variable, fix it.

Change-Id: I2b47c6ce7c6099a6db68c4da108d7c0886c7177e
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/3384
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
(cherry picked from commit c16fb81a23dcfa6ab8331efe1c98a86e4444040d)
Reviewed-on: https://review.lttng.org/c/babeltrace/+/3361
CI-Build: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>