testing/selftests/mqueue: Fix mq_perf_tests to free the allocated cpu set

testing/selftests/mqueue: Fix mq_perf_tests to free the allocated cpu set

The selftest "mqueue/mq_perf_tests.c" use CPU_ALLOC to allocate
CPU set. This cpu set is used further in pthread_attr_setaffinity_np
and by pthread_create in the code. But in current code, allocated
cpu set is not freed.

Fix this issue by adding CPU_FREE in the "shutdown" function which
is called in most of the error/exit path for the cleanup. There are
few error paths which exit without using shutdown. Add a common goto
error path with CPU_FREE for these cases.

Fixes: d3f0d6daebc9 ("tools/selftests: add mq_perf_tests")
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>