Fix: unchecked return value of cds_lfht_destroy()

1412202 Unchecked return value

If the function returns an error value, the error value may be
mistaken for a normal value.

In lttng_tracker_list_destroy: Value returned from a function is not
checked for errors before being used (CWE-252)

Reported-by: Coverity Scan
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I85c994440bc2cd5df0545fd1364dab462f98bc1c