libtraceevent: Fix memory leakage in copy_filter_type

It is necessary to free the memory that we have allocated when error occurs.

Fixes: ef3072cd

 ("tools lib traceevent: Get rid of die in add_filter_type()")
Signed-off-by: Hewenliang <hewenliang4@huawei.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Tzvetomir Stoyanov <tstoyanov@vmware.com>
Link: http://lore.kernel.org/lkml/20191119014415.57210-1-hewenliang4@huawei.com
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>