Because at the destructor we will call close() and that will do the
disable. And we destructors can accept NULL, just like free(), so no
need to check it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/n/tip-i98mcyfkkjh5qp62dle27ac1@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>