sample-trace-array: Remove trace_array 'sample-instance'

Remove trace_array 'sample-instance' if kthread_run fails
in sample_trace_array_init().

Link: https://lkml.kernel.org/r/20200609135200.2206726-1-wangkefeng.wang@huawei.com

Cc: stable@vger.kernel.org
Fixes: 89ed4249

 ("tracing: Sample module to demonstrate kernel access to Ftrace instances.")
Reviewed-by: Divya Indi <divya.indi@oracle.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>