perf kmem: Perform some cleanup if '--time' is given an invalid value

If the string passed in '--time' is invalid, 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
Fixes: 2a865bd8 ("perf kmem: Add option to specify time window of interest")
Link: http://lkml.kernel.org/r/20170916060936.28199-1-christophe.jaillet@wanadoo.fr


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>