selftests/rseq: Fix CID_ID typo in Makefile

Ensure that the basic percpu ops tests are effectively built against
mm_cid.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>