Fix: lttng-events.c: variable may be used uninitialized

Fixes the following warning:
        /home/frdeso/projets/lttng/modules/lttng-events.c: In function ‘print_metadata_escaped_field’:
        /home/frdeso/projets/lttng/modules/lttng-events.c:2563:5: error: ‘ret’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
          if (ret)
             ^

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: If2db5e1ad9782fb49d6d07026976d3d22f89f2ab