perf script: Fix error handling path

If the string passed in '--time' is invalid, or if failed to set
libtraceevent function resolver, we must do some cleanup before leaving.
As in the other error handling paths of this function.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: kernel-janitors@vger.kernel.org
Link: http://lkml.kernel.org/r/20170916062537.28921-1-christophe.jaillet@wanadoo.fr
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>