Fix: flt.lttng-utils.debug-info: omitting copy_field_class_content() return value

Fix: flt.lttng-utils.debug-info: omitting copy_field_class_content() return value

  ID 1401259 (#1 of 2): Logically dead code (DEADCODE)
  dead_error_line: Execution cannot reach this statement: goto error;.

  CID 1401259 (#2 of 2): Logically dead code (DEADCODE)
  dead_error_line: Execution cannot reach this statement: goto error;.

Reported-by: Coverity (various ids) Logically dead code
Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I1b3bb7cba9aec34e6a90386178f99cc505d4da66
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1264
Reviewed-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>