source.text.dmesg: use BT_COMP_LOGE_APPEND_CAUSE

Use BT_COMP_LOGE_APPEND_CAUSE where possible, when returning error
statuses.  Some errors paths due to allocation failure now return MEMORY_ERROR,
rather than ERROR.

Change-Id: I32a15d64538a23406114ef661990928f6f9ed296
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/3243
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>